Loft conversion/staircase/gable wall insulation

[scoobasteve]

Hi,

I'm in early planning stages of starting a full loft conversion (New roof going on next week with Velux windows installed is step 1!)

I've had plans done for the conversion and part of the insulation specification is that the gable walls (Mid terrace) must be insulated with 100mm of rockwool or equivalent. I'm fine with this - means the walls will have to be studded out with 4x2 frame work, insulated then boarded.

The query I have that is troubling me is that the staircase will be installed to run directly above the existing staircase and attached to the gable wall along the left hand side of the stair looking up. All of the looking around on tinternet etc at similar installs shows stairs being attached directly to the brick wall - if I was to do this how would I deal with the fact the wall at loft level is now approx 120mm further in if that makes sense?

Is this normal - I think it will look odd looking up the stairs and seeing in effect five inches of the bottom of the built out wall (Not sure I'm explaining this right!)

Solution I'm thinking of going with is to build out the wall 100mm all the way down where the line of the new stairs will be and along the rest of the first floor landing - the stairs will then butt up to the new built out wall and the gap on the underside of the stairs will be covered by boarding and plaster wnyway. this does mean I will be insulating the first floor as well as losing a few inches of space but will look like a neater finish in my opinion.

Is this a 'normal' solution or am I missing something?

Cheers All
Steve

 

[tony1851]

You are not 'missing something' - it's a common issue in loft conversions when the stairs run up the party wall and immediately above the existing stairs.

The solution I use is to screw three or four thick blocking pieces to the wall, in line with and behind where the new string will go. The string of the new stairs is then screwed to these blocks.

One thing I would query is the thickness of the insulation. Why use glass wool?
50mm Kingspan would be almost as good, with thinner battens.

 

[scoobasteve]

Thanks for reply and as for the 100mm not really sure other than all of the internal walling etc is specced at the same - I guess flexi rockwool slab at 100mm is quite a bit cheaper than 50mm kingspan or similar and space isn't a huge concern.

Now just need to get my head around insulation build up for the roof pitch - needs to be 130mm (60 between, 70 under originally) but as rafters are only about 70mm it seems pointless battening them all out - the ceiling level is going to be flush with perlin level so going to use full 130mm under the rafters.

How would I fix through 130mm insulation into rafters? Or should I counter batten the rafters and put insulation in two layers then bottom layer and p/board can fasten to the counter batten?