All of these material should have similar thermal conductivity properties. The only different will be price and environmental concerns. Sheepswool is environmental friendly while the other two are not. Personally I would go for the sheeps wool but if price is a factor then I would choose the fibre quilt. You should install at least 2 layers (each 100mm or 4 inches thick) of quilt running alternative directions. I'm not a big fan of blow in insulation in attic spaces.1) Fibre glass vs. rock wool vs. sheep's wool.
Sheep's wool guy says it's better insulation and less hazardous. But he seems to be offering only 4 inches, which is below minimum recommendation as far as I can tell. I think if asked to double it he'll be priced out of the job. The rock wool guy says he will blow it into the attic direct from van, whereas everyone else will lay by hand. Any downsides? Is there anything to strongly recommend any of these materials over the others?
2) Soffits.
All of them say they will have to drill holes in wooden soffits and install vents. I presume this is normal.
3) Light covers.
The rock wool guy said that existing recessed ceiling lights will have to be covered by protective covers, at about €8 x 7 lights. Two of the others said no covers required, and one said he would use €1 ceramic flower pots! The lights are low-energy LEDs.
said no covers required, and one said he would use €1 ceramic flower pots! The lights are low-energy LEDs.
4) Access hole.
Apparently to have an installed ladder, the access to the attic has to be widened. However there's limited room for this and may entail moving lights and ceiling smoke alarm. More worryingly, one guy says he'll have to move roof trusses (he called them "hangers" and says they are stopping central roof beam from "dishing", but are not actually supporting weight???). I'm extremely reluctant to let anyone touch these, for fear of turning a €1k insulating job into a €40k roof rebuild. He says he just has to cut it/them and make it/them more vertical. Should I just abandon the ladder/flooring idea?
If you intend to use quilt insulation then you will need to raise the flooring to accommodate enough insulation. This can be done by screwing spacer battens onto the existing ceiling joists and then screwing your flooring on top. Compressing the insulation will reduce its effectiveness. If you don't want to raise the flooring then you need to consider a different material with a lower thermal conductivity such rigid board insulation that can be fitted between the ceiling joists.5) Flooring
Some of the quotes suggested just flooring on top of joists, meaning insulation is either thin or compressed there. Others said floor would be raised using some sort of spacer. What's this all about and what's best?
Thanks for the very helpful replies. I believe one or more of the quotes are also proposing to cut through joists to widen the attic access hole. Is that also a bad idea? Basically, should we get the insulation done and abandon any thoughts of making the attic more accessible for storage?
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