On Fri, 9 Apr 2004 20:54:21 +0100, Steven Briggs
wrote:

Hello all.

This years project looks set to be a large shed at mums place.

I'll be building from scratch, as I want a challenge and to achieve
something better, more substantial and different from the usual stuff.

It'll be about 18' x 8', part potting shed, part summer house, with
covered veranda deck area. There's a CAD render of the design at
http://www.sbriggs.plus.com/shed14.jpg


Nice design - I think she should be very pleased.


I have a few questions for the collective wisdom of the group on
construction methods and materials.


The latest thinking on the base is to mount it on single brick pads (on
a large, existing concrete platform), then a 50x100 joist frame, T&G
floor, then the shed structure.

With this, I wouldn't go for more than 450mm centres.

You will need a matrix of brick piers.

Alternatively, what I did was to start with a concrete base and then
use pressure treated wooden bearers on it and the joists orthogonally
on top of that. It's worth putting some DPC material like Visqueen
down to isolate the timbers from the concrete. You can also use
packing pieces on top of the bearers in order to level the final
floor.



Wall & roof framing I'm thinking 25x75 sawn timber studs & rafters,

I'd up that to 50x75mm for good strength.

50x75 sill & head. Inside skinned with 6mm WBP ply,

I would go for 12mm or even 18mm there because you can fix things to
it. 18mm ply is used in large quantities (or OSB as an alternative)
so it is not that expensive. You will get a much sturdier result.


outside with VT&G
weatherboard.

That's fine.

I'll put about 30mm of Celotex / Kingspan on the inside
face of the wall cavity. I'm debating the need to vent the remaining
cavity to the outside, I can easily have a 10mm hidden gap around the
framing at ground & eaves level, and over the roof ridge board. Is this
a good idea?

Yes. What I did was to tack nail small spacers to the sides of the
vertical studs such that the Celotex front face was level with the
front of the studs. Then I tape sealed the Celotex to the studs with
metallised tape and ply clad on top of that. This created an air
gap behind and ventilation was arranged to the air gap.


Should I put a vapour barrier in there somewhere? If so,
what to use?

Celotex has foil on both sides and you do not need an additional
vapour barrier.

It would also be worth insulating the floor and ceiling.

For the floor, build the floor frame and then tack nail spacers in
the same way as I described for the walls. Drop in the Celotex and
put flooring on top of that. I used 18mm T&G for that.

it is also worth insulating the roof. I used exactly the same
technique for that, making sure that there is ventilation on the cold
side.



Timber treatment is another issue. While the floor joists will be
tanalised timber, I don't think my local timber yard has on-site
treatment plant, so everything else (weatherboarding, frame, floor etc)
will be untreated red or white wood. I could then paint or spray a
suitable preservative on, but would it really be worth shopping round
and getting the whole lot prevac treated (which adds about 20% to the
cost)?

I dealt with this by using Cuprinol Clear Wood Preserver. which is a
spirit based product.

When you get your compressor, get a cheap air powered paint sprayer
and then spray both sides of the timbers. Three coats are recommended.
You can apply any other finish afterwards if you want to.




Any other construction or material suggestions welcome.

Use a very good quality roofing felt. The heavy grade is not a lot
more than the cheap shed stuff and lasts a lot longer.




Finally, this is grand excuse for compressor and nail gun purchase.
Probably the Axminster £100 compressor (2.5HP /25L /7cfm FAD) and 50mm
brad nailer. Are 18ga brads going to adequate for the cladding?

Not really. I used 16 gauge. 18 gauge is normally used to hold
things together for gluing, not for fixing. You need a nailer that
takes 16ga finish nails.




Cheers all,

..andy

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