I need your brains ?

[Dog]

I know there are some very clever people here and I know I'm not one of them so here's my problem, hopefully you'll have the solution ?

I have a cavity wall, the cavity is 15 feet long x 1 foot wide x 7 foot deep. I can buy 15 cubic feet of loose fill insulation in bags, how many bags will I need to fill this cavity ?

 

[Woody Alan]

Dog

I'm sure you're having a "larf" is it the magical number 7

15 feet long x 1 foot wide x 7 foot deep

15 x1 is 15 cubic foot = 1bag.... x 7 = 7 bags

I was always told to show my working out, I'd still get marks even if I was wrong!

OR!!! is the cavity only 4"(which I suspect) not a foot in which case /3 = 2.3 bags

Cheers Alan

 

[Dog]

No, it's an honest and serious question. Old house = very big cavities! Walls are two foot thick built from large granite boulders and at some time in its 300 year existance a breeze block wall was built 1 foot away from the wall and that means a cavity which sucks in and leaks out very cold air during the winter, hence the need to insulate :wink:

 

[Woody Alan]

Then the first part of my answer is serious also. That is a lot of cavity indeed. I would expect the result of insulation will be better than a modern condtruction in this instance, just gyessiong though.

Cheers Alan

 

[Jake]

I'm not sure you'll want to full-fill a cavity like that. The rubble wall is not going to be damp-proof and the insulation will bridge the gap and transmit the moisture to the breezeblock. Try something like the SPAB site or these guys http://www.periodproperty.co.uk/cgi-bin ... /forum2.pl for some more informed advice than mine!

Jake

 

[Woody Alan]

Jake

I am surprised by your reply. I know very little, certainly no proffesional knowledge of building construction, but I was of the understanding that no modern (brick) outer skin is water proof, and that modern insulating materials do not have moisture transmission properties. However always willing to learn.

cheers Alan

 

[Dog]

Cheers both, much appreciated

 

[Midnight]

Dog... I'm not trying to extract the urine... the number of bags required is zero...

that cavity will need to be left as it is... granite block = raydon gas which needs a ventilated cavity to disperse it...

have the same prob, thought the same solution, ran it by the City Archetects dept to get their advise and was shot down for H&S reasons...

Only solution they offered was to build a false stud wall inside the existing one and fill that with insulation...

 

[Jake]

Modern walls are not built full-fill, there is always a gap left in the cavity to break the moisture path, at least that is my understanding. No idea what happens rade.with the cavity wall insulation cowboy trade type of thing. One thing is pretty certain though, and that is that a modern single skin brick cavity will be much much much more rain-proof than an old rubble built wall.

 

[Woody Alan]

The water transmission repellency of the outer skin is not relevant is it? as long as the outer can breathe. All modern bricks are capable of absorbing moisture to a greater or lesser degree. The waterproofness of the cavity wall is dependant on the integrity of the cavity itself, with the design allowing for the escape of moisture should it get through. I would have thought that the "rubble" /granite blocks are more water resistant than a modern brick and and moisture permeability would be through the mortar course. As I have said though I am no professional so I better say no more as I don't think it will add any further value only serving to contradict.

 

[Jake]

Fill the cavity and that is half of the breathing gone. Many rubble walls aren't actually built with mortar at all, as I understand it. More like a drystone wall, pointed with mortar. So they are much more porous than a brick wall, added to which because of their rough surface and prevalence of cavitys, ledges, etc, there is more water around for longer to find its way into the wall. Anyway, I'm no professional either, and have no actual experience of a stone built house, so this is all stuff I've absorbed on the side or dreamt up, while looking for stuff more relevant to my victorian brick renovation project. As I said, SPAB or Period Property will have people who actually know about this stuff!

Jake