Attic insulation

By John Heeran, Energy Advisor

Date:

Tuesday, April 28, 2009

Up TO 30% of heat loss in your home can be lost through your attic. The initial cost of insulation can be high but you will make enough savings on you heating bill to cover the cost of the insulation within two or three years. You should think of it as an investment as it will continue to save you money after that initial cost is saved.

The aim of insulating should be to follow the shape of you living space as closely as possible. If your attic is only used for storage, then you should insulate the floor because if you insulate the roof, you will heat your attic and your energy costs will be significantly higher. If you have an attic conversion, follow the shape of the plasterboard right around (crawlspace floor, walls, diagonal, small attic and back down) to ensure maximum performance.

There are many different types of insulation that can be used in your attic. Each type of insulation has a different K-value (K-value is how the product is rated and U-value is the rating of the roof). The lower the K-value or U-value the better the insulation.

Typical insulation for your attic should be approximately 300mm thick. This is not always the case, a product with a lower K-value or some more advanced materials can be thinner.

Here are some of the most common types of insulation that can be got easily.

Fibreglass - Fibreglass is made from molten glass spun into microfibers. It is probably the most commonly used form of attic insulation and can be got in any hardware store. You will need 300mm in your attic, half between the joists and half over your joists.

Rockwool - Rockwool is made with molten rock instead of glass. This has a better fire rating than fibreglass and would have better acoustic value. Rockwool is a bit more expensive than fibreglass. You will need 270mm in your attic, half between the joists and half over your joists.

Sheep's wool - Sheep have been able to adapt to their many environments as their wool protects them through hot, cold, dry and wet seasons. Wool used as a building insulator retains these properties to create a safe, healthy and environmentally friendly alternative. A pioneering production process first washes and treats the wool with a natural pest-repellant and preservative. The wool is then mechanically bonded into a long-lasting rigid structure which is held together purely by its own fibres. You will need 240mm in your attic. Sheep's wool is a good insulator, but can be more expensive than other insulating materials.

Cellulose - Cellulose is made from shredded recycled paper. This is not used as much as the others but it are a great insulator. This is a good product to help air seal your building as it comes lose and not in rolls, so it fills any awkward areas. The amount of cellulose required will vary due to its density it is installed at. It takes 10 times the energy to produce fibreglass as it dose to produce cellulose.

Hemp - Hemp is a totally natural insulation product available in roll or mat form. This is a good insulator but is on the expensive side but if you care about the environment this is a winner. You will need 240mm in your attic; you could put 100mm between the joists and 140mm over the top.

Reflective foil thin insulation - This is a type of insulation thinner than regular insulation, it is made up of many thin layers of foil with fibrous material between each layer. I would not substitute any of the above products with this. This type of product is not a good insulator but it is good to be used as a vapour barrier as it is a good reflector of heat.

Spray foam - This is polyurethane which is sprayed into your attic. The problem with this is that the timber in the attic needs to be able to breath. It is recommended that at least 50% of the surface of the timber should be open. Unlike the other insulations this would seal the timber and cause rot. So I would not recommend that you put this in you attic.

You must remember when insulating your attic to make sure that you allow an air path into your attic at the eaves. A building needs air to circulate to stop a build up of moisture and stop dry rot. Also if there are spot lights in the ceiling to make sure the insulation is not rolled out on top of these as it could cause a fire. There should be a six inch air flow around each spot light. You could make up a box to place over each spot out of fire rated plasterboard, then you could insulate over that.

It is important to remember that each of these insulations will have a different primary energy, so it will have a different impact on the environment. For example Rock wool production would be high in energy, while hemp would be low in energy. I know price is a big factor in most people's decisions but it also good to consider the environmental impact of each product.

If you are interested in buying an Electric Monitor you can e-mail me at info@thermaloss.ie. This will show you how much electricity each product uses and also how much green house gas is produced.

Hopefully this helped you out.

I must sign off now but you can check in next week for more energy saving news. Don't forget if you have any questions you can e-mail me on info@thermaloss.ie and I will try to include them in my column.

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