Attic stairs insulation

geo88

How much does attic stairs insulation matter?

I'm looking at two stairs options (supply only) :
#1 has a u-value of 0.36 and costs 578e
#2 has a u-value of 0.49 and costs 315e.

What would most people pick? Would the heat savings on the expensive one over 10 years outweigh the bigger initial cost?
Or should I look at stairs that are cheaper but also have an even lower u-value?

The house has a medium level of insulation and the rest of the attic has 100m of old fibreglass insulation that's compacted to about 50-60mm (over several decades..), planning to top up with about 200mm of rock wool.

Lumen

It's a small area so I'd be more concerned with air tightness than insulation values.

Look for an air tightness rating like EN12207 class 4 or equivalent.

Regarding the fibreglass, you're better off taking it out and replacing it with two new layers than just topping up. It's a crappy job though!

listermint

Get an attic stairs cover bag to stop airflow.

Much better option

dathi

here is some maths on your u values assuming a heating season from sept to April thats 8 months or 5400 hours that it will lose heat, mean outside temp of 7* inside 20* =14* difference in temp average size of stairs, 0.6 m2 uvalue 0.36wm2k

0.36w x 0.6m2 x 14*x 5400h /1000w =16.3kwh oil heating aprox 10cent per kwh =1.63 euro per year
0.49 x0.6 x14* x 5400h /1000w =22.2kwh oil 10 cent = 2.22 euro per year


as lumen says you will lose most heat through air leakage through the joint between the stairs and plasterboard if it is not taped properly and through the seal of the door and the frame

geo88

@dathi - wow, that really puts things into perspective, thank you for the math explaining it.
Based on that, as a general rule, one should select the cheapest ladder that is air tight (e.g. passes: EN12207 class 4 as Lumen said).

@lumen: I was going for the topup method due to other recommendations on boards, as it seems more practical. If I were to hire a company to further insulate my attic, my understanding is that they'd do the same and wouldn't bother with removing the old insulation.

listermint

You wouldn't remove the existing you would top up. The existing is fine it's just more compressed.

Besides you'd have to despose of it all and that's not easy either which is why companies don't do it

Cost

Lumen

geo88 wrote: »

I was going for the topup method due to other recommendations on boards, as it seems more practical. If I were to hire a company to further insulate my attic, my understanding is that they'd do the same and wouldn't bother with removing the old insulation.

That's because removing fibreglass attic insulation is a horrible job so nobody wants to do it. :pac:

TBH I don't know that it makes a massive difference. In my case I had a spaghetti of wires all over the place for downlighters and various other unknown purposes, and as I was getting a sparks in to tidy up and replace the fittings with fire rated ones I used the opportunity to take all the crappy yellow stuff out and vacuum the place. Was also handy to see the odd hole I could tape up to help with air tightness.

When the first 100mm layer of earthwool went in it felt immediately much warmer, but since I took the insulation out six months ago I can't say for sure that it is definitely much better.

Anyway, it's the kind of thing where you can convince yourself it's a great idea if you do it, and that it's unnecessary if you don't, so whatever.