You can put all the insulation on top of the roof deck, all the insulation on the underside of the roof deck, or some on top and some below. You can put it all below the roof deck but use two different kinds. Your insulated roof can be a cathedral ceiling or it can be above a conditioned attic.
Yes, you can insulate the underside of your roof. This approach helps improve energy efficiency and comfort by reducing heat transfer. Common methods include spray foam or fiberglass batts. Zavza Seal LLC can guide you on the best insulation options for your specific needs.
Should you leave a gap between the insulation and the roof? Yes, you should leave an air gap between the insulation and the roof to allow proper ventilation and prevent moisture buildup.
The best solution, by far, would be to install a thick layer of rigid foam insulation above the roof sheathing, followed by a second layer of roof sheathing and new roofing. Not cheap, but effective.
Also, when laying down additional insulation, work from the perimeter toward the attic opening. Never lay insulation over recessed light fixtures or soffit vents. Keep all insulation at least 3 inches away from recessed "can" lights, unless they are rated IC (Insulated Ceiling).
You can put all the insulation on top of the roof deck, all the insulation on the underside of the roof deck, or some on top and some below. You can put it all below the roof deck but use two different kinds. Your insulated roof can be a cathedral ceiling or it can be above a conditioned attic.
Can I put plywood over insulation in the attic? Yes you can install plywood subflooring directly over the floor joists and insulation on your floor. You need to install rigid insulation boards on top of the attic flooring joists and then install plywood over the top.
(Source: NRCA.) In the event you are erecting a “cold building” (such as a refrigeration building) that stays at 32 F (0 C) degrees or less inside, you will need a vapour barrier on the outside of the insultation to prevent warm exterior air from entering and potentially damaging the roof's insulation. (Source: NRCA.)
In roofs, the air gap should be larger, typically around 50mm (2 inches), to allow for proper ventilation and prevent condensation. It's important to note that some insulation materials, such as spray foam, do not require an air gap.
If the insulation is installed properly, there should be a 2" air space above the insulation to the sheathing. In all practical purposes, this is should be easy to do if the rafters are 10" deep and the insulation is only 8". If that is the case, the random touching of the insulation buckling up will not matter.
A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel.
Generally speaking, vapor barriers are considered an essential moisture-blocking tool for climates that experience significant levels of humidity. For that reason, building codes in more humid locations will often require them, in which case you might not have much say about whether to install one or not.
Remember that a two-inch breathing space between the insulation and the roof sheathing must be included to allow for ventilation. If I leave room, it's hard to fit more than R-13 without going to rigid foam board.
Yes, too much loft insulation can cause dampness in some situations. Loft insulation works by trapping warm air inside a building, preventing it from escaping through the roof. This helps to keep the interior of the building warmer in cold weather, reducing the need for heating and saving energy.
Properly installing foam board insulation under a metal roof is crucial for optimizing energy efficiency, preventing condensation, and enhancing the overall performance of a building.
To insulate an existing flat roof from the inside, first, inspect the loft for any damage that may need repair. Next, install a vapour barrier to prevent moisture build up. Then, measure and fit the insulation material between the loft joists, starting at the eaves and leaving a 25mm gap for ventilation.
Cold deck roof construction
The cold deck roof as shown above has the insulation at ceiling level and must have a ventilated cavity of at least 50mm. The cavity must be ventilated on two opposing sides by a continuous ventilation gap of 25mm.
The general advice we give is that you should always insulate between and above the rafters (warm roof) or between and under the rafters (cold roof).
Exposed insulation is at risk of catching fire if not covered properly because it is extremely flammable. Installing a fire retardant plastic sheeting over insulation slows the fire damage rate in the case of an adverse event.
Don't: Put Vapor Barriers on the Bottom of the Floor Joist in the Crawl Space. Because vapor barriers are good at retaining moisture, putting plastic sheeting on the joists can cause moisture to build up under the floor.
Although most synthetic underlayments are vapor barriers, there are exceptions.
But the best solution is actually to insulate both the attic floor and the underside of the roof. In this way you prevent the heat from the rooms below escaping to the attic rooms above.
The Golden Rule of Attic Safety
These are the bones of your attic, offering the firm support needed to bear your weight. Ignoring this rule and stepping on the drywall or insulation is a fast track to an unplanned ceiling inspection from below, thanks to our unforgiving friend, gravity.
While both insulated OSB and Plywood offer similar performance in terms of strength and functionality, the Plywood panel is about 7% stronger. As one of the few materials available on the market, insulated plywood is especially suitable for insulating warm roofs.