Loft insulation thickness

[orpheus]

The other thread on insulation materials reminded me - I need to add more insulation to our loft, as the recommended thickness is 270mm.
We have some in between the roof joists, but they are only about 100mm deep. Some installation guides say you must raise the level of the joists, not simply lay an extra layer of insulation material on top of them. Why not? Raising the joists sounds like quite a bit of work.
Anyone done this?

[danmc_82]

Never heard of raising the joists just for insulation. When I do mine in a couple of months it'll be rolled over the lot.

[JimiAces]

for the sake of insulation i would not bother raising the joists. I'm no expert but i imagine that you would only need to do this if you want to lay boards/flooring up there. if its just redundant space i'd just roll it over the top too.

[stephent123]

lay one layer between the joists. Lay a second layer at 90 degrees to the joists. nothing wrong with doing this.

The only reason you may want to raise the joists would be to board out a section of it. If you wanted to board out part of the loft, i would just lay the first layer between the joists under the boards and then put the second layer everywhere else.

[emmiller]

you only need to raise the joists if you are going to floor the loft space as this allows air to flow and keep condensation at bay!

martin

[shoestring25]

when i did my loft i put 3 inch celotex between the joists i wanted to board over this is equal to about 9 inches of normal insulation.

then i put at 90 degrees 8 inch's of normal glass fiber on top of the exiting 4 inches, giving me a total coverage of 9 to 12inches all over.


be sure to get in the eves as most don't and leave 3 or 4 inches uninsulated and thats where all the heat escapes. but this creates a side issue of poor ventilation so be sure to stuff some drain pipe or something in the sofet for air flow in the loft

[Tempest]

what makes me laugh is they say you need a good foot or so on lost insulation.

So then in reality for most people that means they can't store their junk up there.

The best bit is, there should be no electrical wiring under it.

Hmmmm, practical, not

[philbam]

Originally Posted by Tempest

what makes me laugh is they say you need a good foot or so on lost insulation.

So then in reality for most people that means they can't store their junk up there.

The best bit is, there should be no electrical wiring under it.

Hmmmm, practical, not

Good point. I only have about 100mm of insulation throughout the loft but an enormous amount of 'stuff' stored up there - way too much really.However, my roof is always the last one around my street that loses the snow off the roof in winter, meaning that my roof is losing less heat than my neighbours who have the recommended amount of insulation.
I had thought about increasing the insulation but having done a check on ALL my neighbours last winter, have come to the conclusion that my way suits my house (detached) the best.

[Tempest]

Originally Posted by philbam

Good point. I only have about 100mm of insulation throughout the loft but an enormous amount of 'stuff' stored up there - way too much really.However, my roof is always the last one around my street that loses the snow off the roof in winter, meaning that my roof is losing less heat than my neighbours who have the recommended amount of insulation.
I had thought about increasing the insulation but having done a check on ALL my neighbours last winter, have come to the conclusion that my way suits my house (detached) the best.

Well, I'm guessing loads of empty cardboard box's and loads of old crap thae we stuff up there is a good insulator.... LOL

[the whistler]

Electric cables should be over the top of the insulation, and not buried under it. I know its not always practical to do this, but the fact is insulation will prevent heat escaping from the cables with a possible risk of fire. In effect, the current rating of the cable is reduced when insulated which means your 13amp ring main may not be safe to actually carry 13amps.

[orpheus]

Thanks for the responses.

Is it worth buying this Celotex stuff, or are the normal fibre glass quilts ok?

Has anyone taken advantage of the grant you can claim for loft insulation?

[shoestring25]

its only worth doing the celotex if you intend to board out an area other wise normal rag is OK

as for the grant for loft insulation they usually do a really rubbish job don't put it up to the eves don't vent it properly. my mate had his done 2 weeks later the loft was dripping from the rafters. in proper venting condensation buildup. if you want a job done properly do it yourself

also you can usually do the job cheaper than the £150 you pay for it. if your a pensioner or on benefits i think its free

[t72bogie]

the old "measure in inches" is only applicable surely to good old fashioned cheap stuff

modern insulation (like waayyy more expensive) you can have something 50mm thick thats equivalent to 150mm of the old itchy stuff

[shoestring25]

people just say it in inches because its easier to pi cure the measurement than millimeters everything sold is in mm.

10 inches 250mm is the thickness now recommended in the loft

modern insulation (like waayyy more expensive) you can have something 50mm thick thats equivalent to 150mm of the old itchy stuff

solid polyurethane (celotex) is 3 time better that fiber glass i think thats what hes on about

[FZR400RRSP]

My loft has so much insulation in it, it'd be like jumping on a bouncy castle.
Every time there was a BOGOF offer, I just threw more down.
Now that the loft seems (more than) adequately catered for, I'm wondering about cavity wall insulation.
As with most modern houses, the rules and regs have resulted in the builders fitting such a plethora of bloomin' vents that one can feel drafts coming out of skirting boards etc.
Anyone done cavity wall insulation?
What would it (roughly) cost for a 4 bed detached, double garage type property?

I am tempted to cover up some of the myriad of vents as well, it's total overkill.