Loft Insulation and raised tanks

[IJWS15]

House is a little over 10 years old and appears to have 200mm of insulation, some of which has been flattened by storage (now lifted off the joists).

We have two water tanks raised by about 2 feet with no insulation below them and a "wall" of vertical insulation around the space below them. The tanks have the standard plastic jackets with about 15mm of insulation around them.

Am looking at updating the loft insulation, what is the best practice here, Knauf say don't insulate underneath unless the tank is raised (ours are). Don't want frozen tanks but with the little insulation they have that didn't happen in the bad winter three years ago.

Is there really a risk of these freezing? All the pipes have what looks like 2" of insulation (Foam) on them.

 

[AronSearle]

The risk is low, but that is a lot of water to escape should it happen.

I wrapped them in mineral wool, and made a big mineral wool 'box' that sat down with the joists, so the tanks are now essentially part of the internal side of the insulation (kinda).

This was back when mineral wool was £1 a roll, no reason to be stingy with it, took about 2 rolls per tank (I have 4 in my flat loft).

 

[IJWS15]

Tanks now insulated and project proceeds.

Errors by the builders:
- There is a gap between the insulation between the joists and the bit of insulation they put in to join the cavity insulation . . . . explains the damp patch in one of the bedrooms. The gap is now filled.

- In the gable over our bedroom (narrower and smaller) they laid the insulation across the joists. I had wondered but on looking closer there is a40-50mm gap under the insulation all the way across the room . . . Half otf this rectified, back up there tonight.

- There are gaps in the adhesive at the top of the drylining in places so we have a ventilated cavity behind the plasterboard - not for much longer.

In the small gable they have flattened all the spacers meant to keep the air gap open, top of the insulation is damp. Would pushing a coulpe of lengths of 1 1/2" waste pipe over the top of these to restore the ventilation be sufficient? Don't fancy trying to replace the eaves spacers - there isn't a lot of room in there.

Why can't builders do the job properly.

 

[AronSearle]

Why should they bother when customers don't complain and fix the problems themselves

 

[IJWS15]

Why should they bother when customers don't complain and fix the problems themselves

If we'd bought it new the builder would be coming back to fix it. As it is after the first 2 years the NHBC guarantee is next to worthless.

 

[IJWS15]

Job now done

The eaves ventilation was blocked, now some ventilation although most of the plastic eaves ventilation strip was flattened the judicious insertion of short lengths of 40mm waste has helped a lot. The loft is now a lot colder and when windy you can feel the movement! With the light off (3 bulkheads fitted) I can see daylight at the eaves.

Insulation now continuous across the loft and down to the cavity so the gap between the plasterboard and inner skin is covered.

Tanks insulated with 200mm.

Ducting on fans repaired and now under the insulation

Most of roof area has 250-300mm depending on how squashed the old insulation was. Thickness also drops off nearer to the eaves

The bottom layer of insulation in the smaller gable is now in line with the joists so there is no air gap below it.

The boarded area has been raised off the insulation and has an air gap of about an inch between the insulation and the boards. Joists have been extended with timber and the extensions cross braced so they don't "lozenge".

Open topped wooden box with 200mm of insulation in it now rests above the existing downward opening plastic hatch, open the first, put up ladder, lift out second, climb in to loft. Just need to renew the draft seal. Should reduce heat loss.

Overall 8 rolls of 100 and 2 rolls of 200 used. Will see what it does to the gas bill but the house does seem to be warmer when I get up.

Remaining task is to check the "lean to" roof over the dining room to see what the builders did there and update that, only about 8ft deep and no access to the space so may need to strip some roof back to do that.