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Porch, internal door and building regs


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Hello.

 

I've removed an internal UPVC door that separates the house from the porch (see photos).  I understand that if I want to leave this open, then I need to insulate the single skinned porch, in accordance with building regs.

 

My question...will fitting insulated plasterboard over the existing dot and dab satisfy the regulations, or will I have to remove the existing boards, batten and insulate, then re-board?

 

Look forward to hearing from you.

 

Best wishes,

 

Chris 

Door1.jpg

Door2.jpg

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Hard to tell from the photos, but does the current wall buildup have any sort of vapour barrier?

Assuming it does, my concern would be that simply adding extra insulation on top of what's there would lead to condensation forming behind the dot and dab PB, and you can't add a vapour barrier on the inside of the new insulation because that would make a sandwich, trapping moisture.

However if there is no vapour barrier in the existing walls, then possibly you could insulate on the inside of them. I presume you intend to dot and dab a second layer of insulated PB. There might be a limit as to how much weight/thickness you can hang off the previous dot and dab layer.

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This will be classed as an extension to your habitable space, so you need a U value of 0.28 to meet minimum building regs. Or an R value of 3.6.

 

Your single skin brick has an R value of around 0.44 so you will need an R value of around 3.16 for your insulated plasterboard. This means you need a minimum 70+12.5mm insulated celotex/kingspan plasterboard.

 

Have you considered putting a second skin around it or external wall insulation?

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On 11/05/2020 at 12:54, bassanclan said:

This will be classed as an extension to your habitable space, so you need a U value of 0.28 to meet minimum building regs.


That’s for a new element, so wouldn’t they relax the requirement as it’s more of an upgrade/renovation... similar to a garage conversion where a threshold u-value of 0.7 and/or improved u-value of 0.3 are required?

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A garage conversion would also need to meet a u value of 0.3.

 

If you actually want to comply with the regs on this porch then the roof and floor need insulating too.

 

The 0.7 u value  is only for a refurb of an existing dwelling not adding rooms/extensions to it.

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I agree all elements would need to be insulated to meet current u-values. But why would they need to meet the u-values for ‘new’ thermal elements if the elements are existing and are to be upgraded hence needing to meet the threshold or improved u-values?

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The reason is that the elements are NOT existing as part of the dwelling. They exist outside the thermal envelope of the dwelling.

Porches, garages etc are not built to be part of a dwelling, so if they are added to a dwelling it isn't a refurb it's a new habitable space.

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If like you say both porches and garages exist outside the thermal envelope of a dwelling and are therefore not built to be a part of a dwelling, why would the upgrade of a porch wall need to provide min. 0.28 but the upgrade of a garage wall need to provide min. 0.30?

Edited by DevilDamo
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15 hours ago, DevilDamo said:


That’s for a new element, so wouldn’t they relax the requirement as it’s more of an upgrade/renovation... similar to a garage conversion where a threshold u-value of 0.7 and/or improved u-value of 0.3 are required?

I used 0.3 as I was replying to your quote.

A U value of 0.3 was the old requirement for new extensions (which I guess you looked up) it should be 0.28 for both garage and porch and other extensions.

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For loft or garage conversion, you use the u-values as stated in L1B (Table 3) as attached and not those as stated in in L1B (Table 2). Table 3 is in relation to “Upgrading retained thermal elements” and Table 2 is in relation to “Standards for new thermal elements”.

 

This is why I was trying to think why to upgrade a garage wall for a conversion, you’d need to meet the threshold value of 0.70 or improved value of 0.30 but you wouldn’t apply the same criteria for a porch wall!?!

3383F97C-BFD5-4A4C-B2F0-B44A399C466F.jpeg

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