U value applicable to the whole house or just an extension?

[imsparticus]

Hi, we have a detached house which had a double story extension consisting of a double garage with room over capped of with a flat roof. Just to make it clearer the flat roof is raised about 3 to 4ft over the ceiling height and has trusses.

We would like to have a skylight fitted in the flat roof and from what I have read the insulation would have to be increased up to current standards as we would need building regs for the structural aspect.

Now the question is: Is this correct and if so would this apply to the whole of the building or just the loft space above the extension? (The loft of the main house is separate)

Many thanks.

 

[freddiemercurystwin]

The skylight would need to comply with Building Regulations as would any any structural alterations required to insert the skylight. Are you saying that there is a flat roof 3-4 feet higher than the ceiling? The cheeks of the skylight would need to be insulated but you would not need to upgrade the rest of the roof or house.

 

[DevilDamo]

So you have a void of approx. 3ft between the ceiling and flat roof joists?

The roof should already be insulated... either at ceiling joist of flat roof level. If you're proposing a skylight to the flat roof, then you will also need to form a shaft of some sort, due to the void. You don't "need" to submit a Building Regulation application if the works are non-structural, which would mean the skylight/shaft would have to fit between the ceiling and flat roof joists (i.e. 400mm/600mm). In some cases, this distance isn't big enough so there would most certainly be structural implications (i.e. cutting one timber to make the openning 800mm/1200mm) with double joists above and below the new opening. Depending on the BCO, they may ask to see calculations OR they'll be happy with some additional timber without the need in submitting an application for works, whcih would be VERY minor. In that case, it may be best to give the BCO a call and ask them to come out to discuss. At least you have tried to seek advice before carrying out the works, which "could" be un-authorised.

Any new glazing would have to comply with current u-value's (including any necessary background ventilatioN) and be carried out by an approved person/company (as per part L of the Approved Documents).

As mentioned, speak to your BCO to seek advice.

 

[imsparticus]

Thanks for the replies. Yes we have a void above our ceiling which is already insulated at ceiling joist level. I was wondering if we would need that insulation (as it's around 10yrs old) upgraded to meet current levels as we are doing additional work. Or even upgrade the main loft above the rest of the house. I'm not sure where I’ve read it or I may have even misread that if any works are carried out i.e. a skylight then not only does the skylight have to comply with current U values but so does the rest of the roof?

As the joists are just 500mm apart and we would like a large (ish) skylight we would need structural alterations which in turn would mean building regulation approval but I didn’t want to open up a can of worms with the rest of the house.

Once again thanks, I'm off to find our friendly local BCO.

 

[DevilDamo]

There is no need for you to improve the insulation. The BCO will not or "should" not ask for this... at all. They'll only be interested in any structural alterations and the new glazing.

 

[mikric]

There is no need for you to improve the insulation. The BCO will not or "should" not ask for this... at all. They'll only be interested in any structural alterations and the new glazing.

Correct