Insulation Query for Detached garage Conversion

[Yorkshireman]

Hi,

 

We have a 40ft x 16 ft double skinned garage we are looking to convert in to living accomodation. We're aware we need 90/100mm floor insulation and 150mm warm roof insulation but we don't know if there is any form of cavity insulation. What, if any recommendations, would you make regarding internal wall insulation? Cheers for your help.

[Redbeard]

1 hour ago, Yorkshireman said:

What, if any recommendations, would you make regarding internal wall insulation?

 

Do external insulation if you can!!

Does

1 hour ago, Yorkshireman said:

double skinned garage

mean you have a cavity, or is it just 9" (225mm) brick?

 

If it's cavity then you'd want to fill the cavity first (preferably with graphite EPS beads) before you externally insulated, in case of air movement within the cavity.

 

If doing IWI get an interstitial condensation risk analysis done, and consider breathable materials such as wood-fibre or cork rather than PIR. Crudely, you can insulate externally to about half the U value (twice the insulation) that you'd get ('safely' - from a moisture point of view) with IWI.

[Yorkshireman]

It's double skin brick with a cavity [4inch?] 

[Redbeard]

1 hour ago, Yorkshireman said:

It's double skin brick with a cavity [4inch?] 

 

If it's 4 inch you might get a U value of a bit over 0.2W/m2K. I wonder whether you would need to comply with the values in tale 4.2 or 4.3. That governs whether you need 0.3 or 0.18W/m2K. It depends whether it gets classed as improvement of an existing dwelling (it isn't one) or as a 'new fabric element in an existing dwelling' (well, it isn't one of those either!! I'd still go for a 0.18 or better target. It'll cost less to run. You could get the U value down with a little bit of IWI, but consider a condensation risk assessment first.

[Yorkshireman]

I've looked into the EPS beads which I think could be inserted in the cavity via the open top once the roof comes off for full replacement and full planning permission will be submitted as we intend to build an additional room joining the main bungalow to the 'annexe'. We had considered EWI but due to the building being built on the actual boundary we opted against this due to additional factors related to the neighbour. We are looking into the internal condensation/ventilation risk with all windows having maximum trickle vent allowances for their sizes and the same with the french doors but will also look in to having the ICRA done as soon as we can, so thanks for that. The bathroom/en-suite will have an external through wall [between joists] extraction system and the same for the hob, but we are aiming to achieve the best possible U value we can.