Which blocks to use

noseall · Posted: Thu Apr 30, 2009 9:07 pm Post Subject:

Wood floats too.

Shytalkz · Posted: Fri May 01, 2009 3:00 am Post Subject:

noseall wrote:

Wood floats too.

Apart from Natalie Wood

wavetrain · Posted: Fri May 01, 2009 7:39 am Post Subject:

noseall wrote:

Wood floats too.

noseall I did specify a masionry built structure

Shytalkz · Posted: Fri May 01, 2009 7:43 am Post Subject:

Wave, ooi, just how big is this edifice about which you are having extreme concerns re blocks and dpm actually going to be?

wavetrain · Posted: Fri May 01, 2009 7:54 am Post Subject:

MR shy, I think you need to get out in today's sunshine and dig some footings

Shytalkz · Posted: Fri May 01, 2009 8:07 am Post Subject:

That's as may be, but are you going to answer my q?

wavetrain · Posted: Fri May 01, 2009 8:13 am Post Subject:

But why do you feel the need to ask such questions?

Shytalkz · Posted: Fri May 01, 2009 8:22 am Post Subject:

Mountains; molehills; nuts; sledgehammers.

I'm sure that you get my drift.

jeds · Posted: Fri May 01, 2009 10:11 am Post Subject:

clarebear wrote:

Thanks John, that's been very helpful. I think we will probably use thermolite because of the insulation value and because everyone keeps telling me to shut-up about blocks! Out of interest which would you choose?

The proof being in the pudding; I've just used thermolite for my own extension. Although the cavity is only 75mm so had to really to achieve the min U-value, but I'm quite happy about it.

I've specified full fill cavity and partial fill cavity in about equal measures over the years and either is a good method. On balance though full fill is easier for the bricklayers to get right and when I have had problems it is always with poor fitting or badly clipped rigid boards. It's easy enough for a decent bricky but you do get the odd one that cutting somewhere close to a straight line is just that bit beyond them.

__________________
John

freddymercurystwin · Posted: Fri May 01, 2009 1:00 pm Post Subject:

jeds wrote:

It's easy enough for a decent bricky but you do get the odd one that cutting somewhere close to a straight line is just that bit beyond them.

But wavetrain's a self builder, are you suggesting a self builder would accept anything but 100% perfection?

alittlerespect · Posted: Sat May 02, 2009 10:36 am Post Subject:

If your going to fill the cavity with insulation, you will need to reduce its effectiveness to around 80% of the quoted value due to the increase in thermal bridging that will be caused by the insulation being in contact with the external wall, something that you would not get with a cavity. This would increase the overall U value of wavetrains design to 0.31W/m2K.

I know that we are only taking coppers here, but as the saying goes - look after the coppers and the pounds look after themselves!

I am a firm believer in the cavity wall construction, the external wall acts as a sacrificial layer to protect the inside of the building, and avoids the all to common problem of damp penetration which you seem to get all too often with cavity fill (assuming the cavity is kept clear of unwanted material!)

Regards

wavetrain · Posted: Sat May 02, 2009 5:20 pm Post Subject:

ALR, I have not heard of this correction factor being used since the formula for calcaulting U value makes no mention of it.

Can you provide a reference so I can refer to it please?

With regard to cavities, a 150mm cavity would be better, then a 50mm air gap could be incorporated.

I wonder if there are structeral drwbacks to ever increasing cavity widths? IF not one could always turn all these new matchbox detached houses into long terraces for a more cozy feel in the winter.

Shytalkz · Posted: Sat May 02, 2009 5:45 pm Post Subject:

The wider the cavity gets, the less interaction there is between the leaves for lateral loading. At 150, it's effectively two separate walls.

BS EN ISO 6946 has all the info you want, WT. Enjoy the read

BRE sell a handy little gizmo that does all the calcs for you for £50 plus VAT.

^woody^ · Posted: Sat May 02, 2009 7:45 pm Post Subject:

alittlerespect wrote:

If your going to fill the cavity with insulation, you will need to reduce its effectiveness to around 80% of the quoted value due to the increase in thermal bridging that will be caused by the insulation being in contact with the external wall,

How can insulation be a thermal bridge?

Especially when the insulation is the most thermally efficient component of a cavity wall?

wavetrain · Posted: Sat May 02, 2009 8:04 pm Post Subject:

I do hope ALR is not going down the route of punted around by the multifoil insualtion band harking on about having an airspace etc.

low emsitivy surfaces ie foils have not shown any signifcant improvment to U value in any configeration when tested by BRE. The benefit of foil on kingspan etc is a vapour barrier only