Flat Roof Insulation

[Click4]

Hi,

Never realised before until now, that replacing more than 25% of a roof is notifiable to building control.

Now after doing some reading, I understand that part of a replacement or repair job consisting of more than 25% of the surface needs to be insulated to meet the requirements before it will be signed off.

Also from what I understand it is recommended this insulation is 100mm?

So, my next question is...

If you have an existing flat roof, and are re-surfacing it, 100mm is a heck of a lot to add to its height if it wasnt originally designed for it.. the sides are going to be really high!

Therefore, is it possible to insulate like stud walls, and push the 100mm insulation in between the rafters in a tightly fitting manner... or would this not meet the building requirements?

Thanks

 

[noseall]

Therefore, is it possible to insulate like stud walls, and push the 100mm insulation in between the rafters in a tightly fitting manner... or would this not meet the building requirements?

A 'warm deck' system is the simplest way of insulating a flattie whilst overcoming all the problems attributed to cold bridging and venting (condensation).

This usually involves fitting 100mm celotex or similar above the joists then fixing the weathering layers above this insulation layer.

This method deals with thermal bridging through the joists as well as eliminates the need for any venting.

Whilst your method of going between the joists is ok it does not deal with the bridging effect and you will have the problem of shadowing occurring on the ceiling below. You may also not convince some officers that you have fitted it snugly enough to prevent condensation forming on the underside of the deck.

 

[maltaron]

Am I missing something here. Since when has refelting a flat roof had anything to do with the BC. If its a replacement then yes but repair or refelt?

 

[noseall]

Am I missing something here. Since when has refelting a flat roof had anything to do with the BC. If its a replacement then yes but repair or refelt?

A paragraph from Building Control Guidance Note entitled "Repairs and Re-furbishment to External Walls, Roofs and Floors.

"Some repairs to flat roofs will not require an application for approval under the Building Regulations. However, if the roof over a habitable room is to be replaced then you may be required to upgrade this 'thermal element' of the structure..."

 

[Click4]

Building control have been involved in any roof repairs and replacements since 2006.

You need building notification if you are repairing or replacing more than 20% of the surface of the roof iicrc.

Lots of roofers though are ignoring this though and doing repairs and replacements anyway without bco approval.

Thanks for the reply above, from what I gather now there are 2 approved methods.

Warm and cold, warm being easiest as you just add in the region of 100-150mm foam insulation on top of roof deck then redeck and refelt as normal.

Cold roof, you add 100mm insulation between joists, leaving a 50mm ventilation gap above the insulation.. Then underneath the joists install a vapour membrane before installing the plasterboard.. Then add adequate vents either side of the roof to create ventilation accross the roof above the insulation in the 50mm gap.

So warm deck is obviously the easiest and best method for retrofitting.. But due to adding 100-150 mm to the height of the roof you need to have really wide verges around the edge or redo the fascia to keep the usual wodth

 

[paulf1976]

There is also a Competent Person Scheme for roofing, [/url]http://www.competentroofer.co.uk/. If you join the scheme it will...our 'done in a day job' is often problematic!