Though some batts come with a paper or foil facing that can act as a vapor barrier, Tom Silva prefers to use 6-mil polyethylene sheeting, cut to fit between the joists and with seams sealed by foil tape, to prevent moisture from seeping into insulation.
Whether using loose fill or batts, put the vapor barrier closest to the warm side of your installation, where hot, moist air would get in—facing the house's interior in cold climates beneath floor insulation and the attic's interior in hot climates on top of floor insulation.
Some regions don't require a vapor barrier. Fasten blocking around the hatch or door to allow the material to be installed around this area without escaping. Make sure the fill's depth is uniform across the attic. To make it easy to eyeball how level the material is as you blow it in, screw depth guides to joists throughout the space.
To get the target R-value from the product you chose, use the number of bags your calculations showed that you needed to insulate your attic—never fewer. If you've reached your target depth but still have a few bags left over, keep adding the material at an even depth throughout the space until all the bags your calculations called for are empty.
To help the material achieve the right density as you install it, hold the blower hose parallel to the floor and the floor joists. Blow in the fill between and over the joists rather than across them.
Always use unfaced batts, both when laying product for the first time and to prevent moisture from becoming trapped between new and old layers of insulation. You can buy them unfaced or simply remove the paper or foil backing. Place a new layer of unfaced batts perpendicular to the old layer, to cover any gaps in the lower layer.
Adjoining batts should be butted snugly together, but not tight enough to compress them. Never lay heavier batts, such as cotton, over lighter ones, like fiberglass.
You'll compress the lower layer and reduce its effectiveness. Always cut batts to fit around obstructions and penetrations. Stuffing or cramming them around ducts, piping, and the like will compress the air-trapping pockets in the material, reducing its insulating properties. Don't leave any gaps between batts and joists, obstructions, or abutting batts. Even narrow ones will let air escape. Instead, cut a thin strip of the insulation you're using to size. Some pros prefer it to utility knives because the large blade easily slices through the thick material.
Use a piece of plywood as a cutting surface, and stand on a scrap 24 as a straightedge to guide your cuts.
If you're considering turning your attic into conditioned storage or living space, it's worth changing tactics to insulate between the rafters and wall joists instead of the floor. You can use rigid foam panels or do as Tom Silva does with nearly all houses these days: Hire a pro to install spray foam insulation.
Foam blocks airflow needs no vapor barrier and has a higher R-value per inch than loose fill or batts, so you'll get more protection with less depth.
With spray foam, unlike with loose fill or batts, you must cover the soffit vents they aren't needed to keep the roof cool. Then cover the foam with drywall as required for fire safety.
Looking for more help with repairs around your home? A home warranty may help. The more environmentally friendly options include cork, straw and wood board. When making your decision, there are a number of factors you need to consider. The first is the conditions up in your loft - if you know it is draughty up there, it might preclude you from being able to use blown fibre or loose fill insulation.
Cost is also naturally going to be a major factor, which will probably narrow your available choices. Feel free to browse our products right here on our site, or alternatively give us a call on Jun 17, All you need to know on the different types of loft insulation. Recent Posts See All. This type of insulation is ideal for attics with standard spaced beams and joists and very few obstructions. Batts must be carefully trimmed to fit snugly around vents to retain their R-value effectiveness.
Pricing can vary based on thickness and material, but it's generally 0. You can expect an R-value of 3. Loose-fill insulation is great for installing in attics with very little headroom and multiple obstructions such as vents and cross-beams.
It can be effectively blown over existing insulation and is available in fiberglass, cellulose, and mineral wool. Cellulose is the most effective material and has an R-value of 2. Rental is often included for free if you purchase a minimum amount of insulation. This type of insulation is expensive and not a do-it-yourself project, but it has one of the highest R-values at 3. Both types are made with polyurethane. The difference is that closed-cell foam cells are filled with a gas that helps the foam expand to fill the spaces around it.
Open-cell foam cells are filled with air, which gives the insulation a spongy texture.
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