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U valve calcs for bifolds


Cresswelle

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So we’re mid build and builder suggested we put bifolds in across the back of our current and new back wall as will open it up. Must admit not sure why we didn’t think of this during planning but hey ho. 

 

we’ve submitted plans to BC advising them

of the change and included SE calcs and the amended drawings but they are asking for u value calcs as we’ve gone over the 25% glass allowance. I’ve asked the SE and he says it’s the architect who basically has suggested I speak to the head of BC and explain that the level of insulation is increased as we’re having the loft done at the same time and we’ve increased the overall efficiency in the house so this should offset the glass. Does this seem right? 
 

I think the architect is being a bit lazy and generally can’t be bothered. I’ve asked him to make a very small change to the rear elevation drawings as requested by BC but he reckons he’s too busy. 
 

any suggestions how we can get this through. I’ve left a VM for a chat with the building control guy but not sure I’ll get anywhere 

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Bifolds in place of what ..? You may need a non material amendment to your planning if the openings have changed. 
 

Also, you’ll need the SEng to check the lintel and steel sizes for the openings as bifolds have very tight tolerances. 
 

TBH if you just want light, add a couple of full length floor to ceiling windows - 1/10th of the price and much more practical. Bifolds are very overrated …

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So a steel will have a deflection value under load and most SEng will use standard values. That’s normally L/360 which means for a 3.6m beam it can be up to 10mm. That can cause issues with jamming of bifolds so you can ask for a smaller deflection to resolve this. 

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