Adding loft insulation

[Nutkey]

Had someone round to day to add insulation to the existing. They turned up, swore about the guy who quoted originally and left. As I pointed out, if it was easy, I'd have done it myself....

The roof has a 17.5 degree pitch, so there's basically enough space to crawl down the middle - it's 5m wide, so if you do the math, you'll find that's a a whopping 75cm clearance in the centre. Any work close to the eaves requires lying flat and inching along the 40cm span between rafters. Falling through the ceiling isn't an issue - getting stuck is! My wife says the guy who showed up was pretty tall :)

There is currently about 75mm of blown insulation. I can't get too close to the eaves, but I could push the blown stuff to the edges (and therefore increase the height) and then lay new insulation in the central space - starting at the ends, and retreating over boards as I go. I'll probably use the cheapest glass-wool style insulation and aim to go 200mm deep. Any more than that and I reckon ventilation will be somewhat limited.... The area to cover is about 50sqm, so I guess by the time I've shoved the existing blown insulation to the edges, and left a ventiliation gap, I only really need to cover 30sqm.

Anyone got any better ideas/tips?

[RobertL]

What about using slabs of Celotex or the like. You'd get more insulation for a thinner layer and they'ed be easy to push into the eaves. You could lay them on top of the joists leaving the blown fill between them.

Robert

[Cicero]

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You could use 'Space blanket' from Wickes (and B&Q, I think):

is clean (stays wrapped in foil) and can be pushed into awkward spaces with a long pole.

Cic.

[Nutkey]

OK - did some calculations. I need 150mm of celotex to reach a recommended u-value of 0.16. However, I could care less about recommended, since I just want to improve things. Meeting Part L would be nice, but is a minor consideration. Allegedly the u-value of rockwool blown loft insulation is 0.045W/mK, so my existing 75mm depth weighs in at an outstanding .61.

Starting with prices:

Celotex - 100mm (u-value 0.24) - over a tenner per sqm. Spaceboard much the same. That's a non-starter.... Space blanket - 150mm, more like 3 quid a sqm with the B&Q BOGOF. Would give a u-value of 0.29, but I'd need to cover the joists to make that real,as they are only 4" (truss roof, don't you love them). It would still be better than the existing, regardless of what I did.... Space blanket - 200mm - 1.88 a sqm, u-value of about .2

I guess the space blanket in 200mm form wins - even if the foil only goes half way round. It'll let me easily remove sections for sticking a crawl board down as well, and I can stuff those in the gaps over the joists....

Stupid question - why is space blanket laid foil side up?

[js.b1]

By the eaves...

- "Celotex Seconds" - keep cost down

- Push this along with a "broom" or plank on a pole

Elsewhere...

- B&Q or whoever "Space Blanket" elsewhere

- Foil backed stuff looks a bit more interesting

It's not about regs, getting the equivalent of 220-250mm etc of insulation in your loft will make your eyes open compared to having

0-50mm previously. The house will be significantly warmer, noise will be noticeably less, draughts will be reduced due to the cold sink, bake-through in summer will be reduced similarly. If your walls have not been CWI you will actually get a bizarre "solar gain hot house" effect if south facing - the heat can get it and the loft insulation holds it in :-) When you add CWI the temperature is less severe, the internal bricks become an "internal thermal mass" smoothing temperature changes.