Loft Insulation direction

leaphaze

We had a loft extension done about 3 years ago; the extension covers the length of the bungalow, leaving around 2-3 meters of the original loft space at the from and rear. I went into the loft cavity at the front yesterday and was disappointed to see the insulation the builders had replaced was only around 4 inches deep. I intend to top this up.

However, what really surprised me was the insulation wasn’t laid between the rafters but across them. Since the rafters go front to back this was obviously quicker for them, but seems to be inefficient to me since it leaves a gap either side of the rafter which can lose heat to the airflow via ventilation. I intend to cut the existing material into manageable lengths and re-lay it between the rafters.

Am I wasting my time?

Looking around the internet, I found Wickes have a good offer at he moment:
Buy 1 roll get 1 free: 1160mm x 7030mm x 170mm: £33.98
That gives 16 sq mtrs for £33.98
http://www.wickes.co.uk/ROLL-INSULATION/Loft-Roll-Insulation/invt/161209

However, might get it at half-price at the moment:
http://www.hotukdeals.com/search?action=search&keywords=loft+insulation


Anyone know any better deals?

27col

That is a coincidence, I have just this minute come in from Wickes, having bought 4rolls of the stuff you are talking about, for about £68.00. As I intend it as top up it was quite a lot cheaper than anything else that I turned up in the local area. I've been meaning to do it for ages, and the latest fuel prices have finally forced my hand.
If your existing insulation is sitting on top of the joists then it is seriously reduced in efficiency. There is going to be a hell of an air current under it, and the whole principle of insulation is that you have an area of still air. This is formed by the spaces in the insulation. Turn it round as soon as possible and then lay the new stuff at right angles to the joists. Best of luck with it.

latecomer

did you check whether there is other insulation between the joists underneath what they laid? Its normal to lay across the beams on you get to the top of them.

Ps Homebase has rolls of space blankets at half price, I got 4 rolls of 100mm for £40, each covers 13m2

leaphaze

27col wrote: »

If your existing insulation is sitting on top of the joists then it is seriously reduced in efficiency. There is going to be a hell of an air current under it, and the whole principle of insulation is that you have an area of still air. This is formed by the spaces in the insulation. Turn it round as soon as possible and then lay the new stuff at right angles to the joists. Best of luck with it.

Thanks, I agree. Guess what I'm doing next weekend!

latecomer wrote: »

did you check whether there is other insulation between the joists underneath what they laid? Its normal to lay across the beams on you get to the top of them.

Nothing beneath the insulation at all. It just sags down between the rafters.

latecomer wrote: »

Ps Homebase has rolls of space blankets at half price, I got 4 rolls of 100mm for £40, each covers 13m2

That's a great price: 52m2 for £40. I wanted thicker insulation though, and eventually went for Wickes space blanket, which is 150mm thick. Just before leaving home I did a quick search on the internet and (27col: don't read this bit) found a printable 20% off Wickes discount voucher for 04-05/10 on their website. :T

Brilliant. Shows what bargins there are around at the moment.

27col

Ah well. You win some, you lose some.

Airwolf1

Just so you know, current legislation is 200mm, so top it up with another 100mm thickness, and if you ever sell your home etc, this'll be one less thing to worry about.

leaphaze

Airwolf1 wrote: »

Just so you know, current legislation is 200mm, so top it up with another 100mm thickness, and if you ever sell your home etc, this'll be one less thing to worry about.

Well, I'll have the original insulation laid by the builder and re-laid by me. That looks to be around 100mm. Plus the 150mm I've just bought. So 250mm should be enough for current legislation.

But why is insulation available in such odd depths? 100mm and 200mm I can understand. 150mm to maybe top up old 50mm perhaps. But 170mm? Where did that come from? Or is 170mm an old standard?

philweatherall

However, what really surprised me was the insulation wasn’t laid between the rafters but across them. Since the rafters go front to back this was obviously quicker for them, but seems to be inefficient to me since it leaves a gap either side of the rafter which can lose heat to the airflow via ventilation. I intend to cut the existing material into manageable lengths and re-lay it between the rafters.

Am I wasting my time?

The insulation needs to be laid tightly in between joists and you can then lay another load across. It is also good to see if possible to seal any gaps in loft space as birds can get in and mice/rats thrive in fibreglass. If you want to improve insulation value even more you can put 'CeloTex' also known as 'Kingspan' if you cut tightly to rafters it is brilliant for heat retention. slightly more tricky than fibreglass but a lot better.

I would advise a dust mask and overalls either way as not a very nice job.

I will check back on this post tomorrow if you have any questions.

Phil Weatherall (Carpenter)

Airwolf1

leaphaze wrote: »

Well, I'll have the original insulation laid by the builder and re-laid by me. That looks to be around 100mm. Plus the 150mm I've just bought. So 250mm should be enough for current legislation.

But why is insulation available in such odd depths? 100mm and 200mm I can understand. 150mm to maybe top up old 50mm perhaps. But 170mm? Where did that come from? Or is 170mm an old standard?

I think I did a miss type before. Current thickness is 270mm, I don't know what I was thinking off.

And yes, I believe 170mm was an old standard.

philweatherall

But why is insulation available in such odd depths? 100mm and 200mm I can understand. 150mm to maybe top up old 50mm perhaps. But 170mm? Where did that come from? Or is 170mm an old standard?[/quote]

That is because the insulation is not just used in loft spaces, it is usually used in studwork walls although slabs are normally preferred. Also, standard floor joist tend to be around 150-200mm depth.

Phil Weatherall (Carpenter)