Loft insulation - top up to joist top or run across them?

Joined
14 Dec 2010
Messages
31
Reaction score
0
Country
United Kingdom
Hi

I have a reasonable size loft with 50mm of insulation in it and 100mm joists.

Having scoured the web for feedback I'm wondering how best to proceed to get closer to 270+mm.

Everything seems to focus on 100mm between the joists then 170mm run perpendicular to the joists over the top.

To do that, I'd have to lay another layer of 50mm across the loft before running the perpendicular rolls.

Is that my only option? Could I just run the perpendicular rolls or would the air gaps underneath defeat the point of extra insulation?

Would another option be to run 150mm over the existing 50mm between the joists (which would then be 100mm proud of the top of the joists) then run 100mm rolls over that at right angles? (i.e. 50mm+150mm between joists then 100mm rolls running perpendicular)?

Any feedback welcomed.
 
Sponsored Links
Hi

Would another option be to run 150mm over the existing 50mm between the joists (which would then be 100mm proud of the top of the joists) then run 100mm rolls over that at right angles? (i.e. 50mm+150mm between joists then 100mm rolls running perpendicular)?
That sounds like the best option for you and will give you a well insulated loft.
 
What condition is the 50mm in?

Our loft was in a similar state however the insulation down was very dirty and a bit patchy. Given the really cheap deals on insulation around at the moment, I just pulled the old stuff up and put down 100mm + 170mm at right angles.

Filthy, time consuming job (I had about 130m2) but probably worth it in the end.

S
 
Thanks for the replies.

The current stuff is in ok condition, just not very thick.

Hoping to avoid ripping out the existing insulation - a time consuming messy job, as you say.

It's about 80sqm.

Was planning to use "space blanket" which is wrapped in plastic and keeps the dust down to aminimum.
 
Sponsored Links
You could also consider the recycled plastic stuff, it's non-combustible and does not irritate or get dusting when installing, plus environmentally friendly.
You'll want a nice sharp hand saw to cut in to it though
 
There is another option.

Use the existing stuff doubled up over half the loft to bring it up to 100mm and level with the top of the joists. Then fill the remaining half with new 100mm insulation. Finally lay 170mm cross-ways over the whole lot.
 
Thanks all

Opted to rip out the old stuff and put in new 100mm base layer with 170/200mm spaceblanket (bonkers cheap at B&Q at the mo).

Not fun, but at least I know what's up there and what state it's in now :)

Took the opportunity to note down the wiring with the loft naked too...
 
What wiring did you have? reason for asking is if you have socket circuits and/or power circuits such as used by the shower.
They should not be total surrounded by insulation, unless they are current rated safely, and calculation should be factored in concerning method of installation.
Your lighting circuits should be safe providing the fuse/breaker is rated at 5/6 amp.
The ideal situation would be to have your cable laying above the insulation.
 
It's a mix of both. There are 2 power shower feeds, but I've put cross members between the joists to create boxes around them and keep the insulation at least 100mm away. The lighting ring is just laying on top of the spaceblanket.
 
100mm should be sufficient distance to let the heat dissipate.
When having cables routed through thermal insulation for distances over 500mm, the cable can lose 50% of it's safe current carrying capacity. That's why in lighting circuits you usually get away with it, as a standard lighting circuit will be wired in at least 1.00mm2 cable.
This can carry 16 amps, these are normally protected by 5 amp fuses or 6 amp MCBs, which means even when derated by 50 the cable can still carry 8 amps safely and as the fuse/MCB is rated less than that, it should not become an issue.
But power circuit cables are not usually rated 50+% higher than the protective device serving them, so they are normally a problem.
But there are ways around it by doing as you have done, laying above insulation and other insulation methods that I wont bore you with.
What is important is your loft is safe and free from fire hazards.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top