If you have a loft with 4" deep joists & 6" deep insulation, what happens if you board the loft & therefore compress the 6" down to 4"?
Does it still insulate as well as 6" or does it insulate like 4"?
Does 18mm chipboard have much insulating ability?
Well I remembered reading at
At a guess the 6? insulation compressed to 4? will be significantly worse than the 4? alone. The thermal conductivity of glass is around 1 W/mK and that of air is around 0.025 W/mK, about 40X lower. When you compress the 6? insulation down to 4? you?ll have 50% more glass and less air than in the uncompressed 4?. Since the heat is flowing much more in the glass than in the air ? poorer insulation. Insulation is all about having as much air as possible and as little solid matter, whilst keeping the air still so you don?t get convection.
Wood has a conductivity of around 0.1 W/mK so you?ll get some insulation, but it?s not thick enough to contribute a lot.
Regarding compression of the insulation, I have the same view. Sadly, I don't know to what extent. How significant do you think significant is!
As others said 6 will be about like 4". But even 6" is only about R
15, im in the US where R 40 is common and R 60 near optimal, Chipboard might be R 1, not very much at all. Heat loss is mostly up as heat rises so you need the most insulation above your heated area.
Doesn't the fact that the circulation of the heated air is very restricted by the chipboard on top have any effect? ISTR something in this group about that. I know that a v. thin, windproof shell over clothing, even when there's hardly any wind, makes a lot of difference. Also, for a small but noticeable difference, a sheet over a duvet is my way of making a small adjustment without much weight (or effort!) - virtually no insulating properties but, being fine-weave, slows down the convection.
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "The Medway Handyman" saying something like:
Like 4" or less - if it's compressed a lot of the air space out, it's going to be less useful than 'real' 4".
Most everything has been tested for "R" - "U" value, the insulating value. Here in the US chipboard is wood, google wood insulation values, I believe depending on type of wood its near the same as fiberglass per inch. Did you know the colder it gets the less fiberglasses insulating value is, and air movement can kill it like in a open breezy attic.
As others said 6 will be about like 4". But even 6" is only about R
15, im in the US where R 40 is common and R 60 near optimal, Chipboard might be R 1, not very much at all. Heat loss is mostly up as heat rises
Well, most lofts are like that. I wondered if keeping that breeze away from the insulation would make up for the compression.
Having chipboard over the joists will make a difference. Just because it keeps moving cold air from the insulation. Have rigid foam over the joists and chipboard over. The cold bridge of the joists is eliminated.
You shouldn't put anything impermeable on the top of the fibre-glass unless there's a moisture barrier under the insulation. It relies on being ventilated on top to remove the moisture which slowly comes up through it.
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