Closing Cavity and Quin Lites

M

Midgirl

Guest
Hi,

We are up to first floor with our build, using 100mm concrete block, 150mm pumped bead cavity, 150mm quinlite B5.

I am trying to work out what is the best way to close the cavity. Our builder has returned the quinlite block, with 10-15mm left to fill, he says with foam insulation. Our architect says a proprietary closer could be used. I also was in touch with the quin lite technical department, to ask their opinion, as they have a detail using 25mm quintherm to close the cavity along with returning the quin lite block. The technical guy in quin lite, seemed to think it was perfectly ok to just return the quin lite blocks, and said to use timber to close the cavity horizontaly. I was suprised by this, as I am just a newbie self builder who just has information on all this cavity insulation closer from the internet, but I would not have thought that timber would be used to close the cavity, and that you would need some insulation along with the quinlite block to close the cavity vertically.

basically what I would like to know, should we be closing the vertical cavity with at least 25mm insulation or is it ok to just leave about 10-15mm and use the foam ? They will be working on the upstairs windows by next week so want to have this sorted by then, so that it will only be the downstairs windows we will have to retro-fit the insulation if so needed.

Hope this makes sense, I am just new to this, and it is really important to me that we get this right, as we are spending so much on the quinlites, insulation etc,, that I dont want to end up losing the heat through poorly finished cavity closers.


Thanks for any help or advice, and I have searched the internet and various forums and am still unsure as to the best approach.

MidGirl
 
Hi MidGirl

These details should not have been left until now and I am surprised your architect has not provided typical ope details at Head, Jamb, Lintol, Sill and Threshold for all structural and weathering openings in the building.
Despite your comments I find it difficult to believe you have an architect retained for site work when you are asking questions like this.
Detailed questions are difficult to answer remotely, but I will offer a few general principles for your architect to consider.
There are, inter alia, three issues in relation to ope returns in cavity wall construction.

(i) prevention of water ingress and damp at the return
(ii) prevention of fire propagation through the cavity
(iii) prevention of cold bridging at the return

For me the prevention of fire propagation is most important - the others are unlikely to kill you.
This is not an exhaustive list of issues that may need to be considered with your particular form of construction, which is not known to me.
Your architect should ensure that any proprietary closer addresses these and any other issues required by the particular forms of contruction you are using.


ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
 
Thanks Onq for your reply.

We do have an architect, who designed the house and did the planning application, we also retained him to do construction drawings for us and also to sign off on the build. He is not project managing or supervising the build as such, but he has been on site several times already at this stage.

DPC has been put in around all the opes, and the cavity closed with a gap left using the quin-lite blocks (AAC blocks). I did ask the architect about all of this and asked about the detail for the opes, he just said we would find it in the building regulations. I will ask him again to supply the detail as you suggested.

Thanks again.
 
Midgirl,

While I accept you have an architect, the reason I first thought you didn't is that the information you were seeking is what typical working drawing details show.
I have little time for architects who do not fully inform the contractor of the detail to be used and he/she should also inform the client if requested.

Working drawings should show that a particular set of details work, and fully inform those persons who are constructing the building.
Its no enough to say "its in the building regulations" when dealing with Quinn-Lite or AAC blocks, because they are not standard.

They are Autoclaved Aerated Concrete, which you can read about here - http://en.wikipedia.org/wiki/Autoclaved_aerated_concrete
I would be concerned if your builder has been instructed to use standard details on Quinn-Lite/AAC blocks; -

=========================

"Depending on its density, up to 80% of the volume of an AAC block is air.
AAC's low density also accounts for its low structural compression strength.
It can carry loads up to 1,200 PSI, approximately only about 10% of the compressive strength of regular concrete.[4]"

=========================

As I've noted previously in other posts, AAC structure need careful detailing by an engineer to ensure stability.
This is in part because they are not as robust as standard blocks and not as strong either.

For example, even heavy doors fixed to lightweight blocks need special fixing details.
I would be concerned if you were using slim columns or short walls in the design.
You should immediately get a structural engineer to check your design.

You should also ensure the proposed details offer adequate fire prevention and damp proofing performance.
Ask your architect to give a written confirmation of the Fire Resistance of these blocks used in this way.
Check it with Quinn-Lite themselves and your local building control officer - you cannot be too careful.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
 
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