Is 100mm loft insulation sufficient

Danny30

As the title suggests looking to get loft insulation put in but prefer to get 100mm as not to have to get loft legs to floorboard loft. Was just wondering if there really such a big difference in efficiency between the 100mm and 270mm? 

FreeBear

Short answer, the more the better. How much energy you will save over going to 270mm over 100mm depends on several factors (inside/outside temperatures, loft area). Going to 270mm will gain a couple of extra points on an EPC and perhaps save you 250-300KWh per year.

Danny30

Thanks @FreeBear. I will opt for the 200mm maybe then. I have some old insulation I can add it to. Just wanted to order now but some of the insulation says "bottom layer" and some says "top up". Is there any difference between the two? 

FaceHead

Yes, 100mm glass wool is insufficient these days. 200mm is a bare minimum.

If you have nothing currently, an option is 100mm PIR boards. Much more expensive than glass wool, but 100mm PIR will produce a u value similar to 200mm glass wool. 

If it saves you loft legs, a lot of effort and improves head height, it might be worth while to splash out on the materials.

Danny30

Thank you. Would I also need to get protector hoods for the downlights? I have 18 downlights and they are about £6 each so going to add up.

FreeBear

Danny30 said: Just wanted to order now but some of the insulation says "bottom layer" and some says "top up". Is there any difference between the two? 

Bottom layer is (usually) 100mm thick and intended for use between the ceiling joists. The top up layer would be ~200mm thick and goes on top of the 100mm layer. No difference between the two in terms of material, manufacture, or performance. You might find top up rolls are not "pre-cut" like the bottom layer rolls are.

FaceHead said: If you have nothing currently, an option is 100mm PIR boards. Much more expensive than glass wool, but 100mm PIR will produce a u value similar to 200mm glass wool. 

 had been going to suggest PIR/PUR boards, but they need to be accurately cut to fit between the joists and any gaps plugged with expanding foam. Under the eaves, this becomes very difficult. Also gets very, very expensive when compared to fiberglass/rockwool.

ComicGeek

Try and limit the amount of loft that is boarded - helps to keep down the amount of stuff stored which really should be sold/thrown away rather than stored for ever. 

I've boarded a central strip of our loft from gable to gable, with 75mm PIR boards cut between joists. At the time I bought cheaper seconds, but not sure that the same market exists any more.

Cheaper 300mm loft quilt elsewhere which also makes installing by the eaves simpler.

Danny30

So we added 200mm of loft insulation to our old insulation which was about 75mm so should be around the 270mm mark. It was done by a friend who is a builder.

I was expecting a decent difference to be honest however the temperature upstairs how not really improved, maybe .2 of a degree. Is there any possible reason for this?

FreeBear

Danny30 said: I was expecting a decent difference to be honest however the temperature upstairs how not really improved, maybe .2 of a degree. Is there any possible reason for this?

Increasing the temperature of a room can only be achieved by pumping more heat in for a longer period. To gauge the effectiveness of insulation, you need to look at the rate of heat loss. You might notice a small saving with your gas bill (perhaps £10-15 per year), but the outside temperature will mask much of the savings as would small changes in lifestyle.

knightstyle

Are the lights LED? if so then hoods probably nit required but check manufacturers instructions.  If old style bulbs then hoods are definitely needed.

Danny30

They are all LED lights which we installed when having a full rewire. I asked the person who put the installation whether hoods were needed and he said it wasn't necessary. I know the regulations probably say otherwise though.