Blockwork before Windows

[Barney12]

We've got almost a month's delay between our frame being erected and the windows arriving.

Potentially I can get the blockwork started (and finished) during this period.

The windows are going to be installed into the timber frame (flush with the outside of the frame).

We have a 50mm cavity which will be closed.

Can anyone suggest any reason NOT to crack on and get the blockwork done before the windows? I actually like the idea as it lessens the risk of damaging the glazing.

[Mr Punter]

I see no reason why not.  If the windows are the Velfac type - sash is flush with frame - you may even need to render the reveals and heads before the windows go in.  Make sure you account for the frame shrinking 12mm per floor - both with regard to windows and roof.  It is worth clarifying the cill, head and reveal details early on so that the bricklayer can build to the correct spec.

[Barney12]

5 hours ago, Mr Punter said:

I see no reason why not.  If the windows are the Velfac type - sash is flush with frame - you may even need to render the reveals and heads before the windows go in.  Make sure you account for the frame shrinking 12mm per floor - both with regard to windows and roof.  It is worth clarifying the cill, head and reveal details early on so that the bricklayer can build to the correct spec.

 

Thanks. Frame shrinkage is something I hadn't considered. What are the practical issues and methods to redress? Do you need to leave a gap to stop the block work cracking? 

[Roundtuit]

This might be a dumb question, but where abouts does getting the roof on sit in your schedule?

[Barney12]

16 minutes ago, Roundtuit said:

This might be a dumb question, but where abouts does getting the roof on sit in your schedule?

 

Perfectly reasonnable question. During the same 1 month window but with a different contractor. 

 

[Roundtuit]

Ah - good plan.   I ask as I got a bit caught out with this.  I didn't fully anticipate that the weight needed to go on the roof to 'settle' the frame before the brick/block outer skin could go up, and I'd lined the brickies up before the roofers.  Windows went in after, but then they do span the cavity.

[Mr Punter]

12 hours ago, Barney12 said:

 

Thanks. Frame shrinkage is something I hadn't considered. What are the practical issues and methods to redress? Do you need to leave a gap to stop the block work cracking? 

 

The frame will shrink but the blockwork will not.  At first floor level this means that if you initially have, say a 10mm gap around your blockwork at head and cill, this may, after a couple of years, become 22mm at the head and -2mm at the cill.  This has a much larger effect the more storeys you are, so on the ground floor allow for 3mm and 9mm per floor above.  To compensate, leave a very tight gap at the head and a large gap at the cill.  Use an external sealant such as Illbuck Timbermax tape, which will take up the movement without compromising weather tightness.

 

Leave enough of a gap at the eaves so that the roof does not end up sitting on the blockwork after the frame shrinks.  Completing the roof covering and loading plasterboards help the frame compress.  If you have a cladding or tile hanging system fixed to the frame much of the issue is eliminated.

 

 

[Barney12]

On 04/05/2017 at 11:10, Mr Punter said:

 

Leave enough of a gap at the eaves so that the roof does not end up sitting on the blockwork after the frame shrinks.  Completing the roof covering and loading plasterboards help the frame compress.  If you have a cladding or tile hanging system fixed to the frame much of the issue is eliminated.

 

 

 

Well at this rate it looks as though my roof is going to be delayed due to the metal seam (Tata) element, thus at this rate the blockwork will be ahead of the roof!!. Thus what I'm planning to do is load the roof tiles on to the roof and stack across the battens. I'm hoping this will provide the "loading" you describe to help compress the frame?