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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Building Questions >> Insulate an outside wall? https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1389883198 Message started by TrevorP on Jan 16^th, 2014, 2:39pm

Title: Insulate an outside wall?
Post by TrevorP on Jan 16^th, 2014, 2:39pm

Hi, I am in need of some advise.

In my loft, which I am in process of fitting top-up insulation, I have one of the gable end walls which is externally boarded, then battened and then rough screeded. Internally there is no insulation and boarding.

My question is, as this has been like this for around 20yrs, should I leave well alone, or is it wise to install insulation and board over?

I am no expert but I thought that with the secondary insulation now being fitted this may cause some heat in loft space and cause condensation, and as I cannot see any vents thought insulating and board over the better plan.
Appreciate your thoughts on which way to go, as I am unsure.

Cheers
Trevor

Title: Re: Insulate an outside wall?
Post by CWatters on Jan 17^th, 2014, 6:46am

Is the loft insulation between the rafters or the joists?

If it's between the joists then the loft should be ventilated. Usually at the eaves. Ventilation trays/tunnels should be installed to stop the ventilation being blocked by the insulation. Insulating the gable wall won't make much difference.

If the insulation is between the rafters then the loft should not be ventilated and yes the gable wall should be insulated.

Title: Re: Insulate an outside wall?
Post by TrevorP on Jan 17^th, 2014, 9:18am

Thanks for coming back, and no the insulation does go over and cover the soffits. Have had a good look round and can see no vents in the soffit anywhere.
I have seen the you can get and fit vent for soffit fixing quite easily, but thought this would be no good as there is no vent higher to give airflow, am I wrong?

Title: Re: Insulate an outside wall?
Post by woodsmith on Jan 18^th, 2014, 8:14am

Ideally you would have ventilation along the eaves and at the ridge, but if you have no ventilation at all then eaves vents are better than nothing. It depends on the roof layout but you should get some decent cross ventilation.

Title: Re: Insulate an outside wall?
Post by TrevorP on Jan 18^th, 2014, 4:42pm

That's all I needed, thanks, the eves have good 'capping', and I would need scaffolding to get up there and fit a vent cap. So I will go ahead and, a number of vents round the eves.
Thanks for your help, cheers

Title: Re: Insulate an outside wall?
Post by CWatters on Jan 20^th, 2014, 7:18am

It's not essential to have ridge vents unless the loft has been converted. The normal idea is to have ventilation in both eaves/soffits so that the air goes in one side across the loft just above the insulation and out the other side. However you do need quite a lot of those round soffit vents...

If I remember correctly they recommend ventilation equivalent to a slot either 10 or 20mm wide the full length of the roof. To achieve that using round vents you may need as many as 4 per rafter bay. In fact you may even need two staggered rows. That's a lot. Perhaps put in one row carefully positioned so that more could be added.

Vents in the gable walls are also a possibility.

Title: Re: Insulate an outside wall?
Post by woodsmith on Jan 20^th, 2014, 8:31am

You can get strip vents that retro fit on top of the fascia board rather than pepper the Soffit with vent holes.

Title: Re: Insulate an outside wall?
Post by TrevorP on Jan 20^th, 2014, 11:48am

Thanks for that, the ones I have seen are round at 75mm dia. was looking to fit about 6 (between every other rafter). I would think a strip type would need some really careful fitting retro fitting, and from a ladder don't think this would be a safe bet for me?