Insulating an Attic
One way to make huge energy savings is to insulate your attic. However, first you must decide whether you want to create a habitable space. For a habitable attic, the insulation is taken right up to just below the roof tiles, so that the attic space is kept warm. This process is mainly carried out when the attic is being converted into a usable room. In older houses and some new construction, the attic insulation is kept at floor level, and the attic space is left as an open area that is prone to fluctuating temperatures. In this case, the attic is often used just for storage.
Storage Attic (Cold Roof)
You must allow for efficient ventilation in a roof space so that moist air is able to escape into the atmosphere. If trapped in the roof space, the moisture will seep into the insulation and damage it, which will reduce its effectiveness. It is possible that trapped moisture will also rot wood or create a mold problem, further damaging the fabric of the house. The type of ventilation required will depend on the type of roof felt used in your roof.
Cold breathing roof (See blue arrows in image below)
A cold breathing roof has breathable felt below the tiles. This means that any residual moisture in the roof space can penetrate the felt and escape into the atmosphere. However, the felt will prevent external moisture from penetrating the attic space.
Cold ventilated roof (See red arrows in image above)
A cold ventilated roof is built with non-breathable felt, so it is essential to ventilate the roof directly through the eaves. Water vapor is then picked up and allowed to escape through a ventilated ridge or through ventilated tiles. Airbricks may also be used in gable walls.
Creating a cold roof
Check whether a vapor barrier has been installed on top of the ceiling on the surface visible between the joists. If not, you will need to lay one to prevent moisture from rising through the ceiling and creating condensation damage. If the roof has breathable felt, moisture escapes through it. This is a cold breathing roof, shown above left, and here ventilation is less of a concern. If the felt is non-breathable, any moist air will be trapped inside the attic. In this case, you need to ensure that there are ventilation gaps in the eaves. You may need to install vents at the ridge or through tiles. The, cold ventilated roof is shown above right. Some modern ventilation systems are designed to be retro-fitted, while others are designed for new construction projects
Cold roof options
Blanket insulation is the best option for a cold roof.
Option 1 (see image):
Lay a vapor barrier, then blanket insulation. Add another layer of insulation at right angles to this if regulations stipulate.
Vapor Barrier
- If you are installing insulation and vapor barriers yourself, here are a few tips to help you achieve the most benefits when using a vapor barrier:
- Always place the vapor barrier on the warm-in-winter side of the wall.
- If you are adding a second layer of insulation to an attic, do not add a second vapor barrier.
- If the vapor barrier tears during installation, tape it tightly.
Habitable Attic (Warm Roof)
You may think of a warm roof as an insulated extension of your home, and in most cases you will be creating a warm roof in order to convert your attic space into a usable room. Like the main rooms in your home, the ventilation of this space mainly relies on windows and doors, although the entry to the attic may be through a stairwell or a hatch. As in the case of a cold roof, the ventilation design of a warm roof depends largely on whether your roof has been installed with breathable or non-breathable felt.
Warm breathing roof (See blue arrows in image below)
A warm breathing roof has breathable felt below the tiles. No gap is needed between the insulation and felt as long as the insulation is moisture-permeable. This allows moist air to pass through the insulation and then through the felt and out into the atmosphere.
Warm ventilated roof (See red arrows in image above)
A warm ventilated roof has non-breathable felt below the tiles. Therefore it is essential to ensure that there is a ventilation gap between the underside of the felt and the insulation below. A vapor barrier should be used on the warm side of the insulation.
Creating a warm roof
Warm roof options
Install blanket insulation between the rafters. You could also insulate below the rafters to stop them from becoming a “cold bridge,” an area that allows the cold in. If you are creating a warm roof to become a living area, such as an extra bedroom, it will almost certainly require planning permission and need to be checked by a building inspector. In many circumstances you may wish to construct knee walls (shown right) that will make the area appear and feel more like the other rooms in your house. The area behind a knee wall can be insulated and used as storage.
Choose one of the following options (refer to image at right):
Option 1: Lay blanket insulation between rafters. This combines with option 3 and a vapor barrier.
Option 2: Install vapor barrier with a ventilation gap behind it. Specifications vary for this material. Always follow the manufacturer’s guidelines.
Option 3: Install thermal-check drywall. This should be used in conjunction with option 1 or 2.
INSULATION DEPTHS:
The U.S. Department of Energy (DOE) has recommendations for R-values. Visit the website at www.eere.energy.gov to find out the recommendations for your area.
TOOLS AND MATERIALS CHECKLIST
- Laying blanket insulation: Protective clothing, vapor harrier, staple gun, blanket insulation.
- Laying storage decking: Protective clothing, blanket insulation, loose-fill insulation (optional), storage decking, woodworking adhesive.
- Insulating pipes: Protective clothing, pipe insulation plus metal clips or tape, miter box.
- Insulating rafters: Protective clothing, furring strips, blanket insulation, vapor barrier, thermal drywall.
- Insulating stud wall: blanket insulation, drywall.
- Fitting brush and flexible seals: Basic toolkit only.
Continue: INSULATING ATTICS AND ROOFS