Found little to no loft insulation in your attic?
Well that would be a cause for concern! In the UK you are required to have loft insulation and would be a red flag if you were to sell your property. You might have wanted to board your loft to find that you you can still see your joists clearly in the attic. It goes without saying the energy retention with loft insulation is substantially different if you are lacking some.
The following is a brief runthrough of what options you have when it comes to loft insulation.
A few types of loft insulation
I’ll only be discussing ‘cold lofts’ here. This is where you leave the eaves of the roof alone. Confusingly a cold loft will be hot in summer as the roof will let heat in and is uninsulated. There are three types of loft insulation –
- Blanket roll insulation
- Sheet insulation
- Loose fill insulation
I’ll be comparing the first two as the loose fill loft insulation is generally carried out using a machine to blow it in. It’s messy, it’s expensive and not the most secure way.
Blanket loft Insulation
It’s cheap! It’s plentiful! It’s recycled! And it’s most likely what you already have. Glass or mineral wool is what can be used to roll out in between the joists.
Advantages
- You can buy this in different thicknesses to match your requirement. Maybe you already have 50 mm down and you just need to bring it up to regulation? Then this 200 mm roll would work for you. Likewise if you had 150 mm then you could get it at half the thickness.
- It’s the cheapest form of insulation in the market.
- It’s ridiculously easy to apply. You just unroll it between the joists, make sure it lies flat and you’re done.
Disadvantages
- You should avoid having bare skin open to this. The glass fibers can give you an itch that’s never satisfying to scratch. I found my clothes made it bad too so they need washing once you’re done with them.
- Bulky to transport. Not too much of an issue if you’re getting it delivered.
- This considerably thicker to get the same value of heat retention as sheet insulation.
Sheet loft Insulation
They come in a few forms but the trademark name KingSpan seems to dominate the market in this segment. There are non branded equivalents that look very popular so could be a good compromise if you need the least height increase in your loft insulation.
Advantages
- You don’t need to raise the floor for loft boards. This is a huge benefit for using sheet insulation. Because the thickness is well below the height of a joist, you’re not required to squash any of it down to make way for boards. Once the sheet material is down you can start screwing loft boards down anywhere you like!
- It’s neat. Not as in cool, but once in it would sit flush with the surface it sits on. Compare that with the image above and the sea of wool. This would help future maintenance of services that may be in your attic.
- It’s a lot more efficient than glass wool. You need less of it per square metre to have the same energy retention.
- You can also use it in the rafters to make a warm loft room. Unlike the glass wool which can’t be hung, sheet insulation can be held in by the tension between two rafters.
Disadvantages
- It’s a pain to install. You can’t roll this out as the above. It needs to sit between two joists perfectly and be flush along both edges. If you leave gaps then the heat from below will channel through these gaps thus reducing any benefit in what you payed extra for. Therefore you will need to make interesting cuts to keep it seamless. I’d expect even more of this for older properties!
- The cost. It’s a lot more expensive so depending on your overall project budget this could surely make it the limiting factor.
Recommend?
I fortunately didn’t have to add any more insulation for my loft. If I had found myself in a position where there was between 100 – 200 mm glass wool, then I would have simply bought some more glass wool to make the overall thickness as close to 270 mm as possible. If however I found there was less than 50 mm of old stuff then I would have made a compromise and got the unbranded sheet material. This would give me the benefit of not having to raise the loft floor but having to pay a lot more.
Additionally you could even do both. Most people do not board their whole loft out and only do what they need to store. If you have a decent amount of glass wool insulation you could think about removing where you want to board. Replace this with sheet insulation thus allowing you to screw loft boards straight into the joists and saving you a job for raising the floor.