How best to improve attic insulation

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Black Sheep

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We live in a 70's house - standard 4 bed semi. The only attic insulation at present is 100mm fibreglass put in at time of building or shortly after.

Any suggestions on the most effective way to improve this would be appreciated.
 
Ive using Space Blanket. It's probably a bit more expensive than the normal blanket insulation but it's mess/itch free:
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It's available from Homebase and B & Q.
 
It's important not to confuse Space Blanket with Space Board. I was thinking of putting in Space Board over fibreglass but could not get a written confirmation from the manufacturer, Knauf Insulation, that it would not cause condensation. This can arise because water vapour from the house below passes quickly through the fibreglass and then meets the denser polystyrene (which is what Space Board is made from) above. There is some risk, at least in theory, that the vapour could condense on the bottom of the Board wetting the fibreglass over time and reducing its effectiveness. In the end I went for more fibreglass, although I hate working with the stuff.
 
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I think it's wiser to use like with like also and would suggest topping up your existing insulation with another 8-10" of fibre glass. Be sure to turn the roll ends up the gable/ party wall for about 450mm and do not cover electrical cables (insofar as this is practicable) and maintain ventilation gaps at eaves.
 
Many thanks for your suggestions folks but I was just wondering is there any advantage in putting insulation up between the purlins.

I notice you all suggest increasing the insulation on the floor of the attic
 
Unless your rof is designed to accommodate this I would not recommend it; doing so increases the condensation risk unless particular measures are taken to provide adequate ventilation. Such measures could include additional slate or tile vents at ridge level and ensuring that a 50mm gap was maintained between any insulation and the sarking felt/ membrane on the sloped part of the roof. This would almost certainly be a more expensive solution and is probably outside the scope of your average DIYer.
 
Many thanks Carpenter so it looks like we will be adding extra fibreglass on top of the original as you suggest or maybe looking Space blanket as Aeneas suggests.

I'll check out prices and convenience ie. itch free, and get DIY hubby kitted out for the job
 
I think I'd put up with the mild irritation from using the regular unwarapped fibre glass if the price differential is significant. Now is the time of year to tackle this job when the roof space is cool.
 
Black Sheep said:
Many thanks Carpenter so it looks like we will be adding extra fibreglass on top of the original as you suggest or maybe looking Space blanket as Aeneas suggests.

I'll check out prices and convenience ie. itch free, and get DIY hubby kitted out for the job
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In the end I used neither Space Blanket nor Space Board, but unfaced fibreglass (1200mm x 150mm) which I got from an insulation supplier for €26 a roll. Atlantic Homecare are selling similar rolls but with a lower insulation value (R-value) for €29.99. B&Q charge €10.65 for 400mm x 150mm Space Blanket which works out at €31.95 a roll. Space Blanket has an R-value of 3.4. Atlantic's "Isover" is 3.4 also. Crown Insulation 40 has a better R-value at 3.75, as does Owen-Cornings 40 also at 3.75. I used the Owens-Corning product on the basis that it was both cheaper and better. But it's a trade off between better insulation value, cost and itchyness!
 
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We did this job recently, but wanted to keep an area of the attic floor for storage, so we put new 150mm battens running in the opposite direction of the ceiling joists where there was good head height and put 150mm extra insulation between those. Then put B&Q chipboard attic flooring across the new battens. Outside the floored area we put 200mm insulation on top of the existing 100mm.

We used the Knauf space blanket, it was half price in B&Q at the time, (about a month ago), don't know if that offer is still available. Very noticeable upstairs in the house, have already reduced the heating in the morning as we were just too warm.
 
The handy thing about Space Blanket, especially in a house like mine where the roof has a really low pitch, is that it unrolls itself. You cut the outer wrappers, then off she goes. It expands, then that causes it to unroll. Then if needs be, it can be easily shoved along, without any humps.
 
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