DIY conversion of loft into bonus room

[monty77uk]

Hi all,

I'm considering making the loft into a bonus room. It wont be built to regs or used for a bedroom. Nor will it have bathroom etc..

So basically I plan to put a couple of Velux windows up there and board/insulate the floor and roof.

Few questions:

- I've been quoted £1100 for 2 small velux windows, good price? Sounds expensive to me.
- The roof doesn't have felt so the tiles go directly onto the wood slats. I'm guessing I'll need an air gap between them and insulation. How much of a gap? It wont leave me much room for insulation if the gap is large so should I increase the depth of the rafters? Or use flashy super efficient insulation boards? I have a ton of rockwool I'd like to use ideally.

Thank you!!!
Monty

 

[freddiemercurystwin]

Get some more quotes.

Technically you don't need a gap at all if you have no membrane although keeping say an inch gap would be prudent although will be easier said than done if you use rockwool. Adding battens to the underside of your existing rafters is the standard ay to increase the depth. As long as they're not 2x2's or equally pathetic.

 

[monty77uk]

..forgot I'd posted this, thanks for the reply !

I've spoken to a builder and have come up with the following:

- Fit velux window
- Lay 55mm space board throughout loft
- Lay 18mm chipboard panels on top of space board
- Pin rockwool to roof slats between rafters
- Put insulation boards (tbd) at 90 degrees to roof rafters
- Put foil backed plasterboard (is foil backed required?) on top of this

It's a 1930s Semi, approx loft floor area of 40sqm. Floor joists are 4x2" with a couple of extra 4x2" at right angles near the front and rear of the loft space. Roof rafters are also 4x2" with boards then tiles .. no felt. Joist and rafter spacing is around 14".

Any better ways of doing this? It'll be for very occasional office space use and general storage.

Cheers!
Monty

 

[Dhillon]

Sorry to bring up this old post. Monty did you go ahead with the job in the end? I would be interested to know if the builder did anything to strengthen the 2x4 floor joists? I would have thought laying space board and chipboard over the 2x4 joists would have added a lot of dead weight.

My semi has a floor area of 45m2 and I am in the process of boarding the loft. But I am having seconds thought about cross battening with 2x4 timbers and laying chipboard on top due to the weight.

Would be interested to know what you did.