All About Insulation and Ventilation
Improving your home's insulation will save money and increase your comfort. Find out the best materials to use in your attic and walls.
Your home's performance is dependent on the quality of its insulation and ventilation. Huge amounts of energy are lost through poor insulation. This wastes fuel, damages the environment and costs you money. New building regulations require owners to improve insulation, ventilation and soundproofing when carrying out alterations and renovations.
Improving your home's insulation is one of the best overall investments of time and money you can make. Although the initial financial outlay may be quite high, the long-term savings on heating bills will make it worthwhile. You can insulate most parts of your home against heat loss, and even fairly modest measures can make a considerable difference. However, efficient thermal insulation must always go hand in hand with effective ventilation to prevent the buildup of condensation.
Heat flows from warm areas to cold areas, and moves in any direction. In the home, warm air expands and circulates, escaping through walls, ceilings, roofs, windows, doors, fireplaces and anywhere plumbing, ducting, or electrical wiring penetrates exterior walls. Thermal insulation acts as a barrier, reducing the amount of heat that escapes.
The term "U-value" is used when discussing thermal requirements in a house, especially in conjunction with insulation products. The aim is to achieve low U-values: this means that a house’s insulation is efficient. In a new-build home U-values are governed by building regulations, and the type of insulation used will therefore need to meet certain requirements.
Insulating the walls, attic, floors and windows of your home is the most effective way of reducing overall heat loss. However, there are many other parts of a home in which a few inexpensive and straightforward methods can make a dramatic improvement.
If you have a cold-water tank in your attic, make sure that you buy a cover for it, or that you cover it with blanket insulation. To avoid possible water contamination, install a secure seal underneath the insulation. You should also insulate any exposed attic pipes.
Modern hot-water cylinders are usually sold with a layer of insulation pre-fitted. If yours does not have this, buy a cover and fit it over the cylinder.
You should cover any attic traps with a layer of insulation, otherwise all your efforts to insulate your attic or roof space may be undermined by leakage through the hatch or around its edges.
Heat emitted by the rear of a radiator can be lost into or through the wall it is attached to. In the past, it was common practice to fit aluminum foil behind a radiator to reflect its heat back into the room, but now it is possible to buy purpose-made insulating kits to do this job.
Gaps between baseboards and floorboards can cause unpleasant drafts, and those drafts will lead to heat loss from your home. To avoid this, you can use filler or wood moldings to close up any gaps.
Thermal Image of Heat Loss
On a thermal image of a house, the roof shows up as cool and blue, suggesting there is insulation present, but the red windows and wooden slats show heat escaping. Even if you have good loft insulation it is important to consider other areas such as walls and windows. If you are fitting new windows in your home, they must have double-glazed units.
When choosing insulation, take into account the material's cost, ease of use, suitability to your needs and thermal properties (U-value). Bear in mind that greener materials are increasingly being used in this area. The effectiveness of a soundproofing material is based on what it is made of and how and where it is installed.
Versatile and easy-to-use, rolls are usually the same width as the space between joists or rafters.
Retards heat transfer by reflecting heat back to its source and by trapping air in its multiple layers.
6 mil Polyethylene
This waterproof, clear polythene membrane is suitable for use below new concrete or wood floors.
4 mil Polyethylene This polythene sheet plastic is used to stop water vapor from penetrating ceilings and sometimes walls.
Requires a blower, which can be rented. Ideal for small spaces.
Pipe Insulation Use this in a cold roof to prevent pipes from freezing, which may cause costly leaks and damage.
Use to wrap around attic water pipes.
Use to cover gaps along edges when soundproofing.
Used under flooring instead of regular underlayment, this helps to improve a room’s sound insulation.
A rigid board installed below floors but also in roofs for insulation. Adjacent edges interlock using a tongue-and-groove design.
Extruded Polystyrene Board
A rigid board used to insulate concrete floors. It is also bonded under flooring sheets to make storage decking in an attic.
Rigid Board Insulation
This comes in panels and provides a high level of insulation. It is more expensive than blanket or loose-fill insulation.
Used in a continuous layer below flooring, this densely packed material reduces the effects of airborne noise.
This dense soundproofing material is sold in slabs. It can be laid below floors, above ceilings, and within walls.
Recycled blanket insulation is made from recycled plastic bottles. It is both eco-friendly and non-itch.
Recycled loose-fill insulation is a wood-based cellulose fiber that mainly consists of recycled newspaper.
Sheep's Wool Batt
Thermafleece made from 100 percent sheep's wool. It is non-itch and is as easy to use as other forms of fibrous batt insulation.
Wood-based insulation primarily made from forestry waste and sawmill residues. Products are added for fireproofing.
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.
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.
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
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
A cold ventilated roof is built with nonbreathable 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.
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.
Below is a cold breathing roof, and here ventilation is less of a concern. If the felt is nonbreathable, 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: Lay a vapor barrier, then blanket insulation. Add another layer of insulation at right angles to this if regulations stipulate.
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 nonbreathable felt.
Warm Breathing Roof
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
A warm ventilated roof has nonbreathable 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.
Moisture contained by vapor barrier
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 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.
Warm Roof Options
Choose one of the following options.
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.
The Department of Energy (DOE) has recommendations for R-values. Visit the website to find out the recommendations for your area.