Keep the heat in - Section 5: Roofs and attics (2023)

Relatively easy access has made the attic a preferred starting point for insulation for many homeowners, although most other areas, such as basements and uninsulated walls, lose more heat than the typical attic. Even if an attic is already insulated, there may still be an opportunity to improve the home's energy efficiency and soundness through airtightness and ventilation. Air leaks from chimneys, vents, plumbing, and electrical boxes in the attic can be responsible for significant heat loss and lead to a variety of moisture problems. The importance of airtight sealing cannot be overstated. If you're upgrading your attic, read this entire section for helpful tips and other relevant information.

5.1 GENERAL CONSIDERATIONS FOR ALL ATTS

Regardless of the type of attic or ceiling in your home, there are a number of things to consider before you get started. A thorough examination of the following resources will help you develop your retrofit strategy.

Accessibility

Most houses with walk-in attics have a hatch in the roof, although external roof or wall entrances are not uncommon. A hatch must be large enough to bring in materials. Otherwise, or if there is no access, you can use an inconspicuous place, e.g. B. a cupboard, drill a hole in the ceiling. The gable entrances on the outside represent one less opening that has to be sealed airtight and offers the fire brigade immediate access in the event of a fire.

Check the ceiling space for obstructions and freedom of movement. Vertical distances less than 1 m (39 inches) do not allow you free movement. Lofts or roofs with no working area are covered later in this chapter in Part 5.4, Narrow Lofts, Cathedral Ceilings and Flat Roofs.

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In addition to checking for structural problems, also check the condition of the roof structure, siding, siding, and soffit and fascia for signs of moisture problems such as leaks, stains, mold, chipping, or rot. Uncorrected moisture problems reduce the effectiveness of insulation and can lead to structural damage such as wood rot or cracked joists. Mold or rot are clear signs of advanced condensation problems. Identify and fix the cause before adding the insulation.

Moisture can enter from the outside if the roof or connector is damaged. Typical problem areas are weak leaks in a ridge, valley or chimney and ice dam leaks. Pay particular attention to water stains on the underside of the trim or along the joists.

Moisture can also come from inside the house and be carried up to the attic as water vapor by escaping air. Typical problem areas occur near air vents in bathrooms and kitchens that penetrate the ceiling, near smokestacks and chimneys, and in penetrations of wiring and cookware lights. One telltale sign of an air leak is discoloration of the insulation. So don't hesitate to look under the existing insulation to locate air leaks.

During or just after a cold snap, check the attic for condensation, which shows up as frost in cold weather. Some ice build-up is to be expected, but if the accumulation is particularly large (10 mm [2 in] or more), verify that ventilation is in place and not blocked by insulation. Checking the attic during or shortly after a storm will help determine if the moisture problems are being caused by internal or external sources.

Examine existing insulation for type, condition (dry, wet, compacted, etc.), average depth, and coverage. If it is damaged or contaminated by mold or bugs, remove it. However, do not damage the vermiculite insulation (see Section 1.4, Health and Safety Considerations).

If the insulation is wet, do not cover it until the source of moisture has been removed and the insulation is dry. Once the insulation is dry, it's probably okay to leave it in place. It's usually okay to use two types of insulation. Check the insulation depth to determine your insulation value. Compare this to the insulation values ​​recommended in Part 2.2, Heat Flow Control.

Make sure the insulation is evenly distributed and fully covered, especially around the entire perimeter of the attic above the wallboards. Uninsulated areas create a cold spot where the wall and ceiling meet, which can lead to moisture and mold problems.

Existing air and vapor barriers

Homes must have a vapor barrier on the warm side of the insulation. In older homes, the vapor barrier may have been provided by wax paper, kraft paper blankets, or paint. Newer homes often have a polyethylene sheet vapor barrier, but in general very few homes have an effective air barrier.

If there is an air barrier, locate it and determine its condition. Remember that an air barrier must be continuous; Holes or cracks need to be repaired and penetrations sealed. Don't hesitate to strip existing insulation where leaks are found and seal those areas. However, as previously warned, do not damage the vermiculite insulation.

Increased insulation means a cooler attic, which in turn means any vapor escaping into the attic can condense before being vented. An airtight attic is essential to prevent the ingress of moist room air.

If there is no air and vapor barrier, focus on a comprehensive airtight seal. Create an effective air barrier using gaskets, cauls and joints to seal joints between building components. Do not rely on opaque, blown or cast insulation to reduce the need for proper airtight sealing.

5.1.2 Fire and other hazards in attics

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Figure 5-4 Keep combustibles out of an insulated metal chimney

• Storm collar (just tucked in, not sealed)
• 75 mm (3 inch) air gap
• Air and vapor barrier wrapped around the drywall to contact the fire retardant
• Firestop installed from below
• ceiling end plate
• Radiation barrier to keep combustible materials away
• 75 mm (3 in) above insulation
• high temperature caulking

Metal chimneys

Factory built metal chimneys must be kept at least 75 mm (3 in) in contact with the insulation unless otherwise specified by the manufacturer or local authorities. Install a non-combustible radiation shield that maintains a 75mm (3 inch) air gap between the chimney and the insulation. To reduce air leakage, first seal the firewall with a non-flammable sealant at the air and vapor barrier. The top of the radiation shield must also be at least 75 mm (3 in) higher than the existing or new insulation level to be added. To prevent the insulation from falling behind the shield, attach a sealant-free pinch collar to the top of the radiation shield.

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Figure 5-5 Keep insulation away from a downlight by creating a barrier

Minimum distance of 12.5mm (1/2 inch), preferably 150mm (6 inch)

If possible, center the accessory, keeping it at least 12.5 mm (1/2 inch) from the sides and top

12.5mm (1/2 inch) plywood box lined with a refractory material such as B. Drywall or sheet metal to create air space around the accessory; Caulk all joints and edges of the box to minimize air leakage

Minimum enclosure volume – allow for 800 cubic centimeters (cc) per device watt (e.g. a 150 watt device would require a 120,000 cc enclosure)

electrical installations

Work safely near electrical lines (turn off power). Consult an electrician if there are questionable wiring or corroded electrical connections.

recessed lights

Traditional recessed indoor lighting is difficult to seal effectively and can become a fire hazard if covered with insulation. Replace with approved hermetic panel fittings or covers that can be safely installed under the insulation.

animal excrement

If you find a significant amount of animal droppings and bugs in the attic, do not disturb them as they can easily harbor airborne fungi, parasite eggs, and bacteria that can cause serious illness. For more information, see Part 1.4, Health and Safety Considerations.

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Figure 5-6 Sealing the tubing stack

Bunch of plumbing

pipe clamp

Heavy polyethylene strip (pad, seal with acoustic sealant and clamp to ceiling)

5.1.3 Airtightness

Select the following areas:

• Around the plumbing and all other pipes. For plastic pipe stacks that move up and down due to thermal expansion, use a flexible gasket or a polyethylene sleeve attached to a plywood sleeve (see Figure 5-6).
• Around cables or ceiling fixtures penetrating the attic and exterior wall partitions and deck boards (see Figure 5-7 and Figure 5-8). See Section 5.1.2, Fire and other hazards in attics, for handling downlights.
• Around the duct that leads from inside the house to the attic. Seal duct connections with aluminum tape, paint or putty. Seal the gaps where the ducts penetrate the ceiling. Ducts must run under insulation or be wrapped in insulation and protected from pinching. Exhaust fans should always blow outwards, but not directly under eaves openings.
• At the junction of the partitions between the ceiling and the inner wall, pull the insulation to locate and seal the cracks along the inner walls (see Figure 4-4).
• Ensure that at the top of the interior and exterior walls, any attic wall voids are closed (usually by a decking board). Block any open spots in the exposed cavity with a piece of rigid insulation and a joint pad. If the top plate is cracked or poorly seated, use caulk and polyethylene to create a tight seal (see Figure 5-7).
• Around the attic hatches (see Figure 4-7).
• Around the chimney. Building codes require that air spaces between chimneys and the floor or ceiling structure through which they pass be sealed with a non-combustible fire barrier (see Figure 5-3 and Figure 5-4).
• On the edge of shared walls. There is often a gap between the side wall (i.e. the wall shared by units in duplexes, three-family houses and townhouses) and the edge of the attic. Make sure this gap is well sealed. If you suspect air is leaking from a cinder block party wall, hire a contractor to caulk the blocks.

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Figure 5-7 Sealing an electrical box
(Note: See Figure 5-5 for the special case of switch boxes for recessed lights.)

Seal gaps at the top of the interior walls

Fill holes around electrical wires with caulk

Heavy polyethylene sheeting (seal with acoustic sealant and staple to ceiling)

electric box

5.1.4 Ventilation

Attic ventilation serves multiple purposes. It reduces heat build-up in summer, extends the life of the roof and reduces the load on the air conditioning system. After airtight sealing, attic ventilation is your second line of defense against water vapor that may have entered the attic. It guarantees a cooler and better ventilated attic that is less prone to ice dam formation at the eaves.

Houses with pitched roofs and walk-in attics are easiest to ventilate with a ratio of 1 to 300 (see below). This ratio relates to the open area of ​​ventilation, so should be increased if the openings are covered with screens (to keep out insects etc.) and deflectors (to keep out rain and snow) that reduce your open area. Ideally place vents to allow good cross ventilation from end to end and top to bottom. However, while important, vents do not prevent condensation or solve the problems caused by air leaks.

Make sure existing attic vents are functioning properly and are not blocked by insulation, debris, or other materials. You may have to arrange ceiling or reveal openings in the outside area if they are not clearly visible from the attic.

Although an airtight roof greatly reduces the likelihood of attic moisture, building codes still require minimal attic ventilation. The ratio of ventilation area to ceiling area should be around 1 to 300.

Do not automatically increase ventilation. Also, do not use electric exhaust fans for attic ventilation, as they may draw in more air than can be supplied through soffit vents. This actually pulls air from the house into the attic, leading to increased heat loss and moisture build-up. They are also prone to interference, noise and increased energy consumption. Wind-powered rotating roof fans do not create suction and are no more effective than other types of roof fans.

The location of the openings is just as important as their number and type. A mix of types and locations is often best. The following sections detail the best approach for your attic type.

5.2 EASY ACCESSIBLE ATTS

(Video) How to Beef Up Attic Insulation | This Old House

After inspecting the attic and performing any remediation work, first focus on air and moisture control.

5.2.1 Air and humidity control

There are five options for installing an air barrier system in an unfinished attic:

• Focus on air seal
• Install polyethylene over joists
• Install polyethylene between the rafters
• Spray foam between the joists (hire a contractor)
• Spray foam under the roof to create an air-conditioned attic (hire a contractor)

The first option is the most practical, since installing a polyethylene air and vapor barrier in an existing attic is fraught with obstacles and requires great attention to detail. Spray foam, on the other hand, provides airtightness and a first layer of quality insulation that can be completed to the desired RSI(R) level.

If attic renovation is being done in conjunction with interior renovations, the easiest way is to install a new single air and vapor barrier at the bottom of the ceiling joists.

5.2.2 Focus on airtightness

It's a good idea to paint the side of the ceiling space with two coats of oil based paint or apply a single coat of latex vapor barrier paint to prevent vapor movement. Ordinary latex paint is not an adequate vapor barrier.

See Section 4, “Comprehensive Air Leak Control” for detailed information on how to stop all attic air leaks.

Install polyethylene over joists

If the attic is relatively free of chimneys, plumbing, or structural members, consider installing polyethylene directly over the ceiling joists. This method involves the fewest seams and requires less caulking and stapling than other methods. It also leaves the existing insulation in place. However, before laying the polyethylene, seal off any obvious air leak paths.

To prevent moisture retention between the plastic and the ceiling, which can lead to possible wood rot or other moisture-related problems, install at least twice the insulation value over the air vapor barrier (i.e., using the one-thirds-two-thirds rule). ). For example, if the stud height is 89 mm (3 1/2 in) and contains RSI 2.1 (R-12), install at least RSI 4.2 (R-24) on top of the polyethylene.

The main difficulty with this technique is sealing the barrier at the top wallboard, particularly in the eaves where there is little clearance. This area must be securely fenced. Spray foam or hardboard insulation can help fill the gap in this area. Cut the rigid panel to fit between the ceiling joists and extend from the top panel of the exterior wall towards the attic. A second piece of rigid insulation, installed vertically, connects the polyethylene to the horizontal rigid panel. Carefully seal joints or seams between the materials. Two-piece spray foam extension kits (or service from a spray foam company) are also very good for sealing areas around joists and boards.

Install polyethylene between the joists

If obstacles such as A truss roof, for example, makes the above method too difficult, install a polyethylene air barrier or low permeability foam insulation board between the rafters. However, please note that this is a time-consuming and tedious process.

Strip the existing insulation from the area you are working in and set it aside. Cut the foam sheets so that they fit exactly between the traverses. Caulk all edges, gaps and joints. Obstacles such as electrical cables require barrier cuts; Seal them carefully to make the barrier continuous. Another option is to cut the polyethylene strips about 200mm (8 inches) wider than the joist spacing. Apply a bead of caulk to the side of the joists along their length and secure the polyethylene with staples passing through the caulk every 75 mm (3 inches) (see Figure 5-10).

Spray foam between the beams

Spray foam contractors can place closed-cell foam between the joists to seal the air while insulating the ceiling. Any existing insulation and dust must first be removed to allow for a good connection. A minimum of 50 mm (2 inches) is required; complete with another insulation afterwards.

Spray foam under the roof

In this approach, closed-cell spray foam is installed just below the roof surface up to the junction of the roof and exterior walls. This eliminates roof ventilation and creates a so-called hot roof, where the attic becomes part of the air-conditioned (heated and cooled) space of the house. This process may be suitable for some attics, but do not proceed without your building inspector's approval, and then only use a certified spray foam contractor who is familiar with the process.

5.2.3 Installation of insulation

Common materials for use in walk-in attics are ceiling or ceiling types or loose insulation. If there are obstacles above the rafters, such as on a roof truss, it may be easier to place ceiling insulation in the rafter gaps and then use loose fill insulation to create a full insulation blanket over and around the rafters. Loose insulation is good in itself too, especially in uneven or obstructed spaces.

Ceiling or ceiling insulation

Snap the ceiling insulation tightly and without pressure between the ceiling joists. If the beam spacing is not the standard of 16 or 24 inches. (400 or 600mm), cut mats to fit or use loose insulation.

Additional installation tips:

• Butt Bat ends as comfortably as possible.
• Blankets should cover the top panel of the exterior wall but not block ventilation. Allow a clearance of 38 to 50 mm (1 1/2 to 2 inches) between the top of the insulation and the bottom of the roof deck to maintain airflow. Use baffles between each rafter space to prevent it from becoming blocked (see Figure 5-11).
• Insulate above and below the transverse fold by splitting or cutting the blanket to accommodate the transverse fold as shown in Figure 5-12. Alternatively, you can cut a blanket into a series of wedges and then place a wedge under each clamp. With either approach, do not compress the insulation.
• The first layer of mat should be thick enough to completely fill the top of the blast room. The second layer can then run perpendicularly along the joists to block any heat flow through and around the joists (see Figure 5-13). Make sure there are no gaps between the two layers of insulation.
• Fill any awkward gaps or gaps with cotton swabs or loose padding.
• Attach ceiling insulation in the same manner as ceilings. It can be pre-cut with a knife or cut to order. Start at one end of the attic and roll out the ceiling.

loose insulation

• Loose fill insulation can be hand poured or blown onto the air and vapor barrier to a depth greater than the height of the joists. This task can be performed by the homeowner with rented equipment or by a qualified contractor.
• Before adding the insulation, nail sufficient depth indicators (such as a piece of lumber nailed perpendicular to the joist) or mark prominent lines on the truss members so you can easily see and measure the depth of the insulation. Ensure an even depth throughout the attic by leveling the insulation with a board or garden rake (see Figure 5-14).
• Fill in all nooks and crannies.
• Do not block ventilation at the eaves. Prevent insulation from disappearing in the eaves by installing rigid insulation board or a wooden walkway before work begins. Hardware stores sell cardboard or foam deflectors that can be stapled between the joists (see Figure 5-11). Make sure the insulation reaches far enough to cover the top of the exterior wall.
• If the loose fill is deeper than the joists, build an insulating frame (cradle) around the attic hatch to allow it to be filled to the brim (see Figure 4-7).
• Bags of insulating material indicate how many square meters (or square feet) each bag must cover to provide the required RSI value. Calculate the attic area to determine the number of suitcases needed.
• If you hire a contractor to do the work, calculate the RSI you want and verify the insulating bags to be used. You should specify the area that a pocket will cover at the selected insulation value. You and the contractor must then agree on the total number of pockets to use, the expected insulation value, and the minimum insulation depth throughout the attic based on a specific density.
• Remember to seal the attic hatch (see Figure 4-7).
• Caulk and insulate uniform sidewalls in adjacent dwellings (see Part 5.1, General Considerations for All Lofts).
• Do not cover recessed devices unless installed in approved covers.

5.2.4 Ventilation

Ideally, 50 percent of attic vents should be through soffit vents and the other 50 percent should be gable, ridge, or roof vents. Figure 5-15 shows different types of ventilation. Both are suitable when used in conjunction with soffit vents. Ridge vents are preferred where practicable, but should be fitted with deflectors to deflect wind blowing off the roof and prevent water and snow ingress. Occasionally a house only has reveal openings. If so, install ridge, ridge, or roof vents to take advantage of cross-ventilation.

(Video) How to Insulate Your Roof: Insulating Your Attic to Save Energy and Money

5.3 LOW-STOREY HOUSES

Homes with 1 ½ or 2 ½ stories have attics with many small parts that can make access, airtightness and insulation very difficult. If you are unable to access these areas, you may need to hire a contractor. If space is available, the following part provides some guidance on how to do the job yourself.

5.3.1 Air and Steam Control

If you have access to attics, follow the instructions for controlling air and vapor flows as described in Section 5.2, “Easily Accessible Attics”.

Half story homes have an important source of air leakage that should not be overlooked: through the ceiling joists just below the knee walls (see Figure 5-17). This critical air leak area must be sealed flush with the back of the knee wall panel. This can be done by cutting and fitting the foam sheet that fills the ceiling joist opening and sealing with caulk or spray foam.

Another option is to compact the loose insulation between the floorboards and the ceiling below, and ensure an air barrier is installed.

5.3.2 Ventilation

Ventilate the attics above and to the side of the upper floor separately with gable ventilators. Position vents to prevent wind from blowing through the insulation.

A second possibility are gable openings in the area above the attic ceiling and eaves openings in the side areas. This is a good option if the house already has working eaves (see Figure 5-19). A ventilation gap in the rafter section allows airflow between the insulated areas.

If not, you will need to build vents in the part along the rafters to allow for proper ventilation (see Figure 5-18 and Figure 5-19). These openings should be on the cool side of the room, while the warm side can be filled with insulation that can be added to the sloping ceiling section unless other precautions are taken in the renovation process.

5.3.3 Insulation

Spray foam and rigid foam insulation can be used, but blankets are cheaper and easier to work with in tight spaces. If there are electrical outlets (be careful to avoid bumps - and also use this opportunity to upgrade the wiring in that area) or pipes in the knee wall, keep them on the hot side of the air and vapor barrier and the Insulate and seal the air lock and steam around you.

• Treat the attic behind the knee wall and the attic above the middle floor ceiling (see Figure 5-17) exactly as previously described for a standard unfinished attic; Also add an air seal under the knee wall.
• Treat end walls as described in Section 7 "Insulating walls".
• The knee wall can be treated like an unfinished attic (see Figure 5-9), taking into account the fact that it is vertical. Install a combined air and vapor barrier made of polyethylene strips sealed between each stud. Caulking all cracks and penetrations and painting a vapor barrier on the interior surface can also create an air barrier. Then install the insulation and secure it with construction paper, cardboard, olefin board, or chicken wire. Better yet, nail 25mm (1 inch) or more of rigid panel insulation to the outside of the studs to maintain the insulation. This also increases the thermal resistance of the wall section and reduces thermal bridges. An attic wall adjacent to a heated room can also be insulated as a knee wall.
• The part between the joists can be filled with insulation if all penetrations through the roof are sealed and if this is permitted by local building codes or regulations (see Hot roof in Part 5.2.2, Focus on airtightness, Sub-roof spray foam). A warm canopy can wrap around the sloping ceiling and then around the knee wall space. It probably won't be needed in the small triangular upper attic. An insulated sloping ceiling allows the knee wall spaces to be used for storage (which is often the case).
• Exposed foam in accessible areas must be protected from fire.
• Due to the limited space for insulation and ventilation in the sloping ceiling, consider attaching rigid panels directly to the ceiling, then caulking and covering them with drywall. This method significantly increases comfort both in summer and in winter, although it can reduce the free space.
• Some contractors specialize in high-density blown insulation, which helps reduce airflow while improving thermal ratings.

Mansardenfenster

Many 1 ½ or 2 ½ story houses have dormer windows. As described for the knee wall, the attic walls can be insulated with blankets. Dormer windows typically contain many framing members that limit the amount of insulation that can be added. In addition to airtightness, consider tightly packed blown insulation, as well as adding hardboard and drywall insulation to reduce thermal bridging.

Piso

In some houses, the attic is paved even if it is not used as living space. You can insulate it by lifting the floorboards and treating them like an unfinished attic, although some or all of the boards will need to be replaced to maintain the rigidity of the ceiling.

Alternatively, a contractor can completely fill the subfloor space by blowing loose, dense filler insulation through the access holes. air leaks, e.g. B. near pipes and open spaces in eaves should be sealed first. Work with the contractor to ensure the space is filled completely and to the correct density.

SECURITY NOTICE:

Before insulating, check wiring (replace damaged or frayed wiring), recessed lighting, or other heat sources that may be hidden under the floorboards. All heat sources must be protected by insulation or removed entirely.

You probably won't be able to meet the manufacturer's recommended minimums for attic insulation by filling that space yourself. If possible, put some insulation on the floorboards to keep them warm and reduce thermal bridges between the joists and floorboards.

5.4 ACCOMPANYING CEILINGS, CATHEDRAL CEILINGS AND FLAT ROOFS

Learn about methods for isolating difficult areas.

5.4.1 Narrow attics

There are three ways to insulate an attic that is too narrow:

• Insulate on existing roof (see Section 5.5, Ice Dams).
• Add rigid boards and drywall to the ceiling if there is adequate headroom.
• Hire an experienced contractor to blow out the dense fill insulation.

The last two options can also be done together. The first and last methods can be used when headroom is insufficient.

There will likely be no way to install a new laminated material air barrier. If there isn't one already, it should be acceptable to install insulation if there is no evidence of moisture problems, if the humidity level in the home is reasonable, and if air enters the attic through the ceiling and is sealed. You can get extra protection by painting the ceiling under the attic with latex vapor barrier paint (ask paint supplier or manufacturer) or two coats of oil paint.

Make sure the contractor prevents the insulation from getting into the eaves and blocking ventilation. If there are recessed lights, fireplaces, or other heat sources in the attic, take precautions to avoid fire hazards.

Ventilating cramped attics can be difficult due to the difficulty in creating adequate airflow. Where the roof extends beyond the outer walls, soffit openings can be used in combination with roof openings or engineered ridge openings.

Many homes with cramped attics do not have eaves. In these cases, approach the ventilation cautiously. The best approach is to carefully caulk the ceiling under the attic from the inside of the house, and then insulate it without installing additional vents.

If possible, check the attic for moisture problems during or shortly after a mid-winter cold snap. Some frost is to be expected, but if the accumulation is particularly severe, you need to ventilate the room, completely seal all air leaks and reduce humidity in the house. Check with your local building authorities to determine what methods are permitted in your area.

5.4.2 Cathedral ceilings and flat roofs

A house (or part of a house) with a flat roof, cathedral ceiling or other construction without an attic is difficult and requires the services of a qualified contractor.

The main problem with these roofs is the limited space for insulation and ventilation. If insulation is already present in the rafter space, trying to add more may not be beneficial. However, if you decide it's worth increasing insulation values, you have several options. Each option carries some risk of moisture problems or thermal bridges that can reduce the effectiveness of the insulation. A technique involving blown insulation is discussed below.

Part 5.6, Renovations and Repairs, covers interior and exterior renovations, including adding a new roof. The existing gap between ceiling and ceiling can be sealed with cellulose or glass fiber insulation on site. Densities are typically between 56 and 72 kg/m³ (3½ to 4½ lb./cu.ft.). The contractor must calculate and confirm the density for each roof void.

This approach eliminates roof ventilation and is therefore generally not recommended (check with local building authorities first). However, the high insulation density combined with extensive air sealing should reduce airflow enough to avoid condensation problems.

Make absolutely sure that air leaks at the ceiling are sealed from below. This is difficult because cables and pipes often pierce the ceiling in several places. In addition, partition walls must not be completely closed at the top, so that large volumes of air can flow through the inner walls to the ceiling.

Where interior walls are completely open to the ceiling there is no easy fix unless you are willing to fill your interior walls with insulation and caulk along all trim, exits and other penetrations.

5.5 ICE DAMS

Ice dams are large masses of ice that typically form on the underside of a roof and in gutters. As melting snow (or rain) trickles down the roof, it hits this mass of ice and retreats, sometimes under the clapboards and then into the attic.

An ice jam usually occurs when there is a significant amount of snow on the roof. The snow itself, especially if it is deep, can act as an insulator. When the attic temperature is above zero, it heats up the roof covering, which melts the layer of snow that is in direct contact with the roof. Meltwater runs down the roof until it hits the overhang.

When the air and overhang are below zero, the water on the roof freezes and starts the ice dam. Additionally, dark, south-facing, sun-warmed siding can allow warm convection currents to penetrate the eaves and roof areas above, causing ice jams.

5.5.1 Roof Type and Ice Dams

Uninsulated attics usually do not have ice dams because the heat flowing through the attic tends to melt the falling snow and prevent it from building up too much. A well-sealed and insulated attic will result in a cool roof and typically will not have ice dams. Ice dams are more common when many valleys and dormers complicate the roof or when there is a large overhang. More complicated roof types retain more snow because they are more likely to have more thermal bridges and air leaks.

5.5.2 Location of areas prone to ice dams

One way to find ice jam-prone areas is to look at the roof after the first hard frost in the fall or light snowfall. Observe where the snow melts first and find out what is underneath that spot. A common sight under these conditions is a horizontal melt line on the roof of a 1 1/2 story home where the small knee wall meets the ceiling. Other locations would be under a roof exhaust fan, plumbing vent, under a skylight, and over a leaky attic access hatch. The best prevention of ice jam is to seal and fully insulate any air leaks in the attic.

Dark wall coatings can absorb solar heat and cause warm convection currents in the walls that can be responsible for ice dams. Caulking the associated soffit openings can help reduce the problem. However, further ventilation may be required to ensure the attic space is adequately ventilated.

5.5.3 Dealing with restricted attic space

Many attics, even those with a low pitch, do not have enough space for adequate insulation at the edge of the attic. If the soffit insulation requires a baffle to maintain venting to the fairing, there may only be about 100mm (4 inches) of space left for the insulation. This limited level of insulation allows snow to melt just above the overhang and encourages ice build-up.

Try to put as much insulation on this edge as possible to reduce heat loss. Spray foam is ideal because it both seals and insulates air. Cutting pieces of extruded polystyrene is also helpful. Place a piece of extruded polystyrene 25mm (1 inch) from the panel to maintain the ventilation gap, and then fill insulation between this foam sheet and the attic (see Figure 5-22).

5.5.4 Cathedral ceilings

Ice dams on cathedral ceiling roofs are more difficult to solve as they are more difficult to access. The same principles apply to preventing ice dams - stopping air leaks in houses, improving insulation, possibly improving roof ventilation. Ice dam problems on cathedral roofs are usually best solved by hiring an insulator with experience in dense pack insulation or roof renovation.

5.5.5 Installation of a new roof

When renovating a roof, remove the roofing and cladding, seal the cavities, and fill the cavities with insulation. Then install the new roofing materials, including an anti-ice membrane. A well sealed roof requires little or no ventilation. If you are unsure whether the sealing can be effective, leave a vent duct under the soffit panel to the top. Insulation can sometimes be added to the inner ceiling, although this approach will not stop the air leak.

An alternative measure to prevent ice dams is to seal the roof with a self-sealing membrane under the roof tiles. Building codes require such membranes on the underside of the roof in new homes. These membranes do not stop ice dams, but they do prevent water from seeping through the roof covering and into the home. Ice jam can still occur and potentially damage shingles and gutters.

5.5.6 Quick fixes and their limitations

There are many popular and faster solutions, but they have disadvantages:

• Connecting electrical heating cables will melt channels in the ice, which sometimes eliminates a problem, but they use a significant amount of electrical energy and are an eyesore on most roofs.
• Removing the gutters will prevent them from becoming ice traps, but the gutters will keep roof water away from the foundation.
• Attacking ice dams with an ax or ice pick every winter will damage the roof surface.
• While removing snow from the roof is also helpful, removing ice and snow dams is not always easy or safe.
• For some older homes with intricate roofs, it may be impossible to completely eliminate ice dams without resorting to various techniques.

The preferred solution for most homes is to keep the heat of the home out of the attic with airtightness and insulation.

5.6 RENOVATIONS AND REPAIRS

Renovations or repairs provide an opportunity to ensure a well-insulated attic ceiling and walls with an effective air and vapor barrier.

A popular renovation measure is the conversion of an existing unfinished attic into a new living space. Depending on the depth of the rafter space, achieving the high recommended Attica RSI values ​​can be difficult. If you decide to finish your attic, check your local code requirements and consider the following steps:

• Attach braces between each pair of bolts (see Figure 5-23). These connections will support both the roof and the new ceiling.
• Ensure that the insulation installed in the joist gaps fits snugly against the walls to form a continuous thermal envelope. There should be no gaps around the attic, otherwise heat will escape and ice jams may occur near the eaves. In most cases it should be possible to insulate every room from joist to eaves and across the outside wall. Leave a gap between the top of the insulation and the bottom of the roofing to allow for roof ventilation. Seal all roof openings in unheated parts of the attic.
• Staple a continuous polyethylene air and vapor barrier to the jambs and posts of the bulkhead; Then carefully seal edges and seams with acoustic sealant.
• If your attic is not very tight, consider bracing the underside of joists and wall joists to allow for more insulation (up to the minimum recommended attic insulation level, if possible). After installing the insulation, nail or screw the tabs (2 x 2 or 2 x 3 on the edge) into existing voids perpendicular to the joists and studs. Place the tapes according to the width of insulation you will be using. However, the braces should not be more than 610mm (24 inches) apart - measured down the center - or you will have difficulty attaching the inner fairing. Fit the insulation snugly between the braces, covering all studs and bolts. Finally, staple a continuous sealed polyethylene air and vapor barrier to the tape. Alternatively, attach 1 to 2 in. (25 to 50 mm) rigid insulation board to studs and studs, caulk or apply a vapor barrier and cover with an approved finish (e.g. drywall).
• The insulation between the collar loops is applied underneath in the same way, with a continuous polyethylene vapor and air barrier being applied last. If the collar loops are already insulated and there is access above, further insulation can be added as for a regular loft.

5.6.1 Suspended ceiling

With adequate headroom, building a drop ceiling to maintain insulation is an excellent way to thermally upgrade a cathedral ceiling or flat roof, especially if planned as part of a renovation. Below are several options:

• Build a new roof directly under the existing roof. If the roof has exposed beams or joists (usually for decorative purposes) it may be possible to close off the space, creating a new roof. Install blankets or rigid insulation in the room, followed by a continuous air and vapor barrier and a new roof. In any case, you need to prevent hot air from entering the new cavity and bypassing the insulation. Caulk the perimeter of the new ceiling and any possible air leak paths through the bulkheads.
• With the roof removed, extend existing joists or trusses to accommodate additional insulation. Cross existing joists or extend the joist cavity with 2 x 4 wood and plywood spandrels (see Figure 5-24).

While it's not necessary to remove interior trim and expose joists and wall tops when building a new ceiling, it's a good idea. This allows you to seal air, check the condition of the insulation, and check for a vapor barrier.

• Mechanically fasten hardboard insulation directly to an existing ceiling construction. While this technique saves you the mess and time it takes to tear down the ceiling, it complicates access to the space between the ceiling and the attic (e.g. to install recessed lighting). If the rigid panel insulation acts as an air barrier, fit the panels tightly and seal the seams well. Expand the electric lights to accommodate the depth of the new ceiling.

5.6.2 Add a new roof

The insulation can also be applied to an existing ceiling or ceiling. This option is best suited for cathedral ceilings and flat roofs where major exterior changes are required, such as B. a new roof. Airtight sealing, installing new insulation, siding, roofing, and replacing eaves, soffits, and eaves, and disposal will cost several thousand dollars. You will almost certainly need the services of a qualified contractor.

One method is to install a rigid insulation board over the existing roof (see Figure 5-25). The higher RSI value of rigid insulation means less increase in roof thickness, although multiple layers of insulation may be required to achieve the desired RSI level.

As an air and vapor barrier, the polyethylene film is first laid on the existing roof according to the 1/3-2/3 rule. Alternatively, a layer of closed-cell spray foam or a rigid, low-permeability sheet can be taped at the joints to prevent air leakage. This step is not necessary if an airlock is already installed.

It is important to insulate (i.e. block) and seal the gaps between the rafters along the perimeter of the roof. This will prevent heated air from escaping around the insulation. Align the edges of the barrier material with the inner lining of the outer wall and caulk all seams thoroughly. Another approach is to hire a spray foam contractor familiar with air sealing to block these critical areas.

Another method is to build up the existing roof or frame a new roof and fill it with ceiling insulation or loose insulation which is then blown in. Make sure the air and vapor barrier is well sealed. The new roof space or structure may add structural stress to the entire assembly so this must be done in accordance with local codes.

This approach is best accomplished with new trusses or by installing trusses (called purlins) that span the length of the roof. Once the purlins are in place, the new studs are installed, followed by the proper installation of insulation to prevent air movement and thermal bridging. Leave enough clearance above the insulation and above the new roof joist to allow for ventilation.

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