Flat built into shed

[herrmnnn]

Hello all,

first post, hope this is in the right spot. Sorry for the long post!

Signed up yesterday but been lurking for a while beforehand. Done some searching, hours of browsing, and found some great info. Would now like some advice to make sure I'm headed in the right direction...

We have a 9mx18m steel portal frame shed on a rural property, in good condition, on good concrete slab. The previous owner lined part of one end, and put a rudimentary bathroom in (toilet, basin, shower and f/g recess - all waste out through wall). I now want to expand on what he did, and make a basic but comfortable flat for a teenager (and visitors once all the kids have left home).

I'm thinking something like this:
85101

Bottom, top and LHS of image are shed walls, RHS is remainder of shed (which is north).

Some questions:

1. Will it be cheaper, and maybe easier (?) to attach gyprock lining directly to the 3 existing shed walls? I will put insulation batts between steel cladding and lining, but what about heat transfer through the metal framing? Or should I run vertical timber battens over shed girts to attach gyprock to, then box around the shed columns?

2. Shed is 3m to gutter, ceiling height will be 2.4m so it would be great to have mezzanine above for general storage. How do I find out what size rafters I need to span the 6m? I found the span tables on this site but can't work out which one to use or how.

3. New timber stud wall (RHS of image) should be made of 75x38mm treated F14 timber - am I reading the tables correctly? Back of wall would be lined with ply or similar, so does this add to structural strength enough to make any difference?

4. I'd like a floating timber floor in living area, carpet in bedroom, but budget may not allow that up front. What should I paint the floor with to prevent damp coming through concrete slab (although there appears to be builders plastic under it) so it's clean for now and allows floors to go straight down when we get the cash for them?

5. Would anyone care to offer a guess as to what the framing and lining materials might cost? :D

Cheers

Tim

[pinger]

1. Will it be cheaper, and maybe easier (?) to attach gyprock lining directly to the 3 existing shed walls? I will put insulation batts between steel cladding and lining, but what about heat transfer through the metal framing? Or should I run vertical timber battens over shed girts to attach gyprock to, then box around the shed columns?

Whilst it may be tempting to screw off gyprock to the back of the shed frame, I would definitely advise against it. Sheds are lightweight steel structure that are designed to move and exploit the memory of the metal to return to their position. Without additional battening they are not suitable to be gyprocked and it will crack.

The cheapest way to do it would be to add 20mm ceiling batten at appropriate centres running floor to eave to provide cross braced strength and correct centres ready for gyprock. As you point out you will need to box out where the portal columns "sit into" the shed.

Your other option (more costly but easier to gyprock) would be a fully independent stud frame flush with the inside edge of the c.

Regardless of what you do, insulate insulate insulate. There will always be thermal transfer in steel structures but your batts in the cavity and gyprock will minimise this.


2. Shed is 3m to gutter, ceiling height will be 2.4m so it would be great to have mezzanine above for general storage. How do I find out what size rafters I need to span the 6m? I found the span tables on this site but can't work out which one to use or how.

The chicken and the egg question.

Mezzanine engineering is tricky unless you know the weight and subsequent dead load of the materials to be stored, or if you are engineering for a trafficable floor.

If it is simply lightweight storage I would suggest a C200/24 would be sufficient for a bearer. C150/15 joists running in the other direction at 600 centres, with 22mm aquatite treated structural flooring. Screw off with 8-18-35 countersunk WingTeks.

Can't help with 3 or 4, I'm a steel shed builder, not a chippie.

Best of luck, the floor plan looks like a teenagers (and parents for that matter) dream. :U

[herrmnnn]

Whilst it may be tempting to screw off gyprock to the back of the shed frame, I would definitely advise against it. Sheds are lightweight steel structure that are designed to move and exploit the memory of the metal to return to their position. Without additional battening they are not suitable to be gyprocked and it will crack.

The cheapest way to do it would be to add 20mm ceiling batten at appropriate centres running floor to eave to provide cross braced strength and correct centres ready for gyprock. As you point out you will need to box out where the portal columns "sit into" the shed.

Your other option (more costly but easier to gyprock) would be a fully independent stud frame flush with the inside edge of the c.

Regardless of what you do, insulate insulate insulate. There will always be thermal transfer in steel structures but your batts in the cavity and gyprock will minimise this.



The chicken and the egg question.

Mezzanine engineering is tricky unless you know the weight and subsequent dead load of the materials to be stored, or if you are engineering for a trafficable floor.

If it is simply lightweight storage I would suggest a C200/24 would be sufficient for a bearer. C150/15 joists running in the other direction at 600 centres, with 22mm aquatite treated structural flooring. Screw off with 8-18-35 countersunk WingTeks.

Can't help with 3 or 4, I'm a steel shed builder, not a chippie.

Best of luck, the floor plan looks like a teenagers (and parents for that matter) dream. :U

Thanks pinger.

Good point on the steel movement - an independent stud frame might be the go... also researching Structural Insulated Panels which look interesting...

Mezzanine storage would only be light stuff, but I know how that can add up... over-engineering sounds like a good plan.

Yes, a teenagers dream... I have a 17yo daughter who will probably be left home for uni by the time this is finished, but also a 15yo daughter at home who will most likely stay home for uni, then my partners 8yo daughter and 6yo son to follow, so I figure it will get a fair bit of use for the next 12 years or so. Not a bad investment from a parents point of view :)...

[pinger]

You should be able to push the spacings out on your timber frame as it will be non load bearing, it is only carrying the gyprock.