30m² Internal Area (Building Regs) and Studwork

[mikkymo]

I'm planning a double garage/workshop in my back garden which will meet all of the planning permission regs, but to save me the hassle of complying with building regs (most of it will), I want to keep the internal area below 30m2.

I have a prefab post and panel type concrete garage which I'm going to put up which will initially have internal dimensions of 6.0m x 5.5m (33m²). The plan is to create a 'room within a room' using studwork, resilient bar, plasterboard and insulation which will add 150mm to each wall and bring the internal area down to 5.7m x 5.2m (29.6m²).

I appreciate that it's a sizeable workshop (18' x 20') and although my neighbours are aware that it's going up and happy enough (we're not overlooked on any side), I predict that we will get a visit from an inspector, particularly if said neighbour sneaks in and measures the dimensions of the outside walls.

My reason for the sound proofing is to completely minimise any sound from me tinkering on cars and it will have the added benefit of keeping heat in the garage. It's not intended to be a 'fake wall' which can be taken down or a place to practice Death Metal music. The honest intention would be that I if I wanted to, I could run an angle grinder inside at 10pm and not hear it outside. No harm no foul and all that.

Will a building inspector think I'm taking the proverbial by having such thick studwork or does it purely go by the internal floor area regardless of the reasons for the studwork? If I take pictures of the sound proofing/studwork going in will that satisfy them that it's not a fake/removable wall?

 

[tony1851]

You need to be careful; the inspector could argue that the internal lining is not part of the structure (ie it could be removed and the garage would still stand).

Your intention of cutting down airborne noise may be reasonable, but do most domestic garages have thick sound-proofing? - possibly not, and that's how an inspector may see it.

 

[mikkymo]

That's a really good point on it being freestanding. At the minute, my design has a steel brace running around the tops of the posts made from 100mm equal angle. That also acts as a wallplate for the trusses to sit on.

I could build an internal wooden frame so that it supports the trusses, effectively giving me a wooden shed clad with concrete posts/panels, but that defeats the sound proofing element.

From looking at recording studios / Death Metal practice rooms, to be 'soundproof' the studwork needs to be loosely attached to the walls (resilient bars) with rubber/cork under it at floor level, then insulated, plasterboarded and sealed. It can then move independently from the outer structure.

If my internal wooden frame is supporting the trusses (i.e. structural), any sound which hits the internal walls will be transmitted into the frame, then into the trusses and out through the roof.

Building regs introduction says:

" “floor area” means the aggregate area of every floor in a building or extension, calculated by reference to the finished internal faces of the walls enclosing the area, or if at any point there is no such wall, by reference to the outermost edge of the floor;"

"Finished Internal Faces of the walls" = ?

What does 'finished' mean in this case?

If I wanted to build a garage / Death Metal practice room - is there anything which would stop me? Surely Metal Heads need a place to practice? I'd happily keep a guitar and an amp in there...

 

[freddiemercurystwin]

Or just build the bloody thing how you like and ignore the silly letters that may/or may not come from Building Control.It'll never go any further than some letters.

 

[theprinceofdarkness]

If the BC gets stroppy, just insist that the 6" thickness is to get the correct U value for your insulation. Now that's being PC. Oh yes and do put some insulation in the wall void and ceiling or that argument will fail.
Frank

 

[mikkymo]

"Finished internal face" apparently refers to whatever covering you put on the internal face of the wall, so if you build it out of block, you can finish by just painting, plastering, plasterboard, studwork and sheet, whatever.

I think the concern for BC is that 30m² is a reasonable amount of space. More than that = more span, more roof area, more drainage requirements, more to go wrong = more ways for people to hurt themselves.

Hopefully I should be fine with taking 6" for the sound proofing.