Head height for room in a room loft conversion

[tomhillonline]

Hi all,

Would very much appreciate some advice. I'm considering the feasibility of a loft conversion where the initial head height availability is 2.3m. I'm (probably) looking at a room-in-the-roof conversion with Velux CAMBRIO style windows rather than a dormer due to Planning constraints. I've got an architect and from conversations with him I reckon that I can make the stairs work.

My questions are:
* If I'm willing to pay (reasonably) over the odds, then what's the most efficient solution from the perspective of maintaining head height; and
* People's general sense of the usability of the space post conversion (I should note that I live in Oxford, where houses are generally pricey and small).

In terms of the spec, the most efficient solution I've seen from a joist perspective is the 195mm referenced by FreddieMercurysTwin in a previous thread (see attached). I *think* that's measured the the bottom of the current ceiling? If so I reckon that means that I'd only lose about 500mm from my current configuration...

In terms of the rafter insulation everyone seems to reference the need to use ~90mm Kingspan PIR style over the rafter, but is there a reason that I couldn't use Spacetherm instead? I haven't modelled it, but from looking at the technical details it looks to me like I'd be able to shave off at least a third off that, maybe a little bit more (since it incorporates a thin plasterboard).

If so, then my losses should be:
- 500mm from the floor joists; plus
- 600mm from the Spacetherm plus say 10 for the MgO board plus plaster.

Gives an estimate head height loss of 1000 to 1200mm? That'd leave a post conversion head height of about 2.2m along the pitch of the roof...

Am I being naieve/over optimistic here?

Many thanks in advance, Tom

 

[freddiemercurystwin]

What planning issues do you have that prevents the obligatory rear dormer? Who will be using the loft conversion? Someone who's 6'6"? Do they spend hours of the day walking about up there or just get dressed/undressed? Otherwise why are you fussing about a few inches here or there.

 

[Wayners]

I took roof off and dropped new bespoke roof trusses on.
They were 190mm deep. 190mm x 2 for floor and ceiling=380mm
Add on 50mm for 25mm roof straps and 25mm batten for plasterboard, then the 12.5mm plasterboard.
I barely made the 2m height for regs.
I actually didn't by 4mm but it never got picked up.
Velux windows X3 are twice the size I needed creating rain noise and heat in summer.
Id fit just one small fire scrape velux given the option now and build in a vent for a cheap mobile aircon unit. £1000 of insulation and its still baking in loft room come summer.
Wish I was detached so I could raise roof height

 

[freddiemercurystwin]

I barely made the 2m height for regs.

What 2m height for regs? The only headroom minimum with regards to lofts is above the stair.

 

[Wayners]

That's how I read plans.
Looking online it maybe because the landing is the same height as bedroom ceiling. Landing has to be 2m.

I can't see how landing can be a different height to bedroom.

 

[freddiemercurystwin]

A bedroom can be lower. There is no minimum headroom for a loft room

 

[cdbe]

Just lower the ceiling in the room below.

 

[freddiemercurystwin]

Just lower the ceiling in the room below.

Drunk again?

 

[cdbe]

Drunk again?

Slightly. But still don't understand why that's not a great idea. But absolutely willing to learn from people like you, noesall, woody, tony1851 etc

 

[freddiemercurystwin]

Think about it, the logistics/costs etc ....