loft insulation - grants available from council?

[Archie_tect]

Well, I may have a problem, in that my loft was insulated a long time ago (at least before I moved in 10 years ago), but it's not as thick as what is now recommended. The problem is that the loft is boarded with floor panels (chipboard panels, loose, not fitted) and the new, thicker insulation won't fit under it - i'd need to either remove the floor panels completely or somehow raise the level of the floor. I'd prefer to keep the floor panels, because I use the loft for storage.

Maz, depending on the arrangement of the rafters and whether it is a modern trussed rafter or a traditional truss and purlin roof, you may be better insulating with batts to the underside of the existing rafters providing you don't leave any gaps between the batts BUT you MUST maintain at least 50mm clearance between the outside face of the insulation and the underside of any obstruction or the sarking felt, or the tiling battens if no sarking, to maintain the ventilation of the cold side to remove the moisture which as it cools passing through the insulation will condense out on the nearest surface. Ventilation removes this effectively. It may be necessary to introduce additional roof ventilation at the eaves and ridge if you do line the u/s of the rafters but this will then give you a 'warm' roofspace which means your loft storage boarded area can remain- best get local advice to check it out

Just one cautionary note on roofspace storage: most ceiling rafters are not designed to take additional load so check the size and spacing of the ceiling rafters before you put too much weight on them. Any cracking of the ceiling or opening up of plasterboard joints is a sign of too much weight on the rafers. If you do put things in the loft best place them over walls below or against walls where the rafters can cope ....certainly not in the centre of the cieiling rafter spans. If in doubt get a structural engineer to check the loadings. A rough rule of thumb for joist depths for domestic loading is half the span in feet plus 2 inches for floor joists and half the span in feet + one inch for rafters... ie a 3m span= 10 feet: half the span +2 inches requires a 7 inch by 2 inch joist [175x50].

 

[Maz]

Maz, depending on the arrangement of the rafters and whether it is a modern trussed rafter or a traditional truss and purlin roof, you may be better insulating with batts to the underside of the existing rafters providing you don't leave any gaps between the batts BUT you MUST maintain at least 50mm clearance between the outside face of the insulation and the underside of any obstruction or the sarking felt, or the tiling battens if no sarking, to maintain the ventilation of the cold side to remove the moisture which as it cools passing through the insulation will condense out on the nearest surface. Ventilation removes this effectively. It may be necessary to introduce additional roof ventilation at the eaves and ridge if you do line the u/s of the rafters but this will then give you a 'warm' roofspace which means your loft storage boarded area can remain- best get local advice to check it out

Just one cautionary note on roofspace storage: most ceiling rafters are not designed to take additional load so check the size and spacing of the ceiling rafters before you put too much weight on them. Any cracking of the ceiling or opening up of plasterboard joints is a sign of too much weight on the rafers. If you do put things in the loft best place them over walls below or against walls where the rafters can cope ....certainly not in the centre of the cieiling rafter spans. If in doubt get a structural engineer to check the loadings. A rough rule of thumb for joist depths for domestic loading is half the span in feet plus 2 inches for floor joists and half the span in feet + one inch for rafters... ie a 3m span= 10 feet: half the span +2 inches requires a 7 inch by 2 inch joist [175x50].

Thanks very much for this.
In my case...Not a modern roof - house built 1945. Traditional truss/purlin. Yes, it has sarking felt.
How wil the batts (these are rectangular blocks of insulation as opposed to rolls, right?) stay in place if they are to fix to the underside of the rafters? Won't they fall out under their own weight?

 

[Archie_tect]

Depends which ones you get... if you got the rigid polystyrene or Celotex RR sheets with tongue and grooved board edges they would give you really tight joints. fixed with skew nails to the rafters incorporating plastic discs to spread the support holding the insulation in place. Less rigid batts may need the equivalent of plastic 'chicken wire fixed to hold them in place again with skew nails and discs.

Alternatively you could beef up the floor joists to extend your living space into the loft area [get an engineer to check the supports and advise on loading/sizes],you could then line the u/s of the roof rafters with insulated composite Gypsum/Celotex or Polytherm plasterboard but you'd probably be best using 'duplex' boards [which include a vapour check foil backing] to reduce moisture transmission. Make sure the eaves to eaves cross ventilation space is maintained over the purlins and underneath the ridge board though to avoid trapping warm, moist air pockets.

 

[summerdays]

We increased the depth of our rafters so that we could fit the insulation in ... it took Mr Summerdays several months doing all the work - he hates the fibre glass stuff so used other versions. But I've since been to an exhibition where it showed some little plastic feet that were put onto the rafters to support the flooring.

In Bristol this weekend ... and I gather in a couple of other towns is a Green Doors event where you can go into other peoples houses to hear what they have had done whether it's insulation or water harvesting or MVHR and how expensive or distruptive it was. I'm going to visit some today.

 

[Andrew_Culture]

We live in a proper sacky area and for a while we were wondering just how many more times we were going to be given free loft insulation, it's looking like a hamster's cage up there now!

 

[asterix]

Some one went door to door around our area.. When they found out we weren't on benefits and we'd have to stump up £100 or what ever it was toward the cavity insulation they were shocked when we wanted to go ahead! Still a bargain at that price..

I'd done the loft myself with 2ft of insulation not long after moving in. Think that cost me just over £200 for the rolls..

2 feet!! You mean 60 centimetres of 2 feet!!!

Where do you put all your stuff?

 

[Archie_tect]

Terry,
With that thickness of insulation in the roofsapce, next winter on a breezy day, feel to see that you're not getting condensation forming in the upper layers [is it glass fibre?] and that you can still feel a cross breeze within the roofspace. If you can feel moisture that's because 'interstitial' condensation is forming within the insulation as the warm moist air rises up through the insulation and moisture condenses out as it cools.

You need to keep a good cross flow of air in the roofspace, keeping the existing vents or slots in the roof eaves clear with at least 50mm of clearance to the u/side of the roofing felt or slates/tiles, so that the moisture is carried out by the cross ventilation and doesn't hang around in warm wet pockets of air which could lead to rot in the timbers.