Self-build summerhouse / office / playhouse?

It's not a strip around the whole edge, you can use less if you do a total of four parallel strips which will divide your floor area into three bays approx 3.0mx3.33 (for a 3mx10m structure) This will give a total of 12m of strip rather than 26m which is a lot less digging and concrete

Since posting I have given the height of the suggested foundation some thought and you could make it lower as follows.

Assuming the level you have now excavated to has removed all topsoil, dig the 4 foundation strips down from this level say 300mm wide by 150mm deep.

These can then be filled with concrete, a couple of lengths of reinforcing bar 2" up from the bottom would do no harm. To get the concrete level hammer some metal or even wood pegs in to the excavation and set the tops of the pegs level with a spirit level & straight edge or a water level. If you then fill the strips with concrete until it comes level with all the pegs.

Again to keep the height down you could lay the blocks flat or even just use a course of bricks. The wickes blocks will be fine.

Thank you, makes a little more sense now. You have to take it very slow for us knuckle draggers .

So 4 strips the width of the build spaced equally along the length. 15" deep, 12" wide. Filled with concrete preferably with reinforcing bars (couldn't find these on wickes, are you able to point me in the right direction?).

Then a course of blocks followed by DPC layer (is the DPC attached to the blocks in any way?) then 4x2 on each strip of blocks (what do I attach these to the blocks with?).

From here I use 150x50 (6x2?) to span the between strips (distance apart?), then add rigid insulation between joists (what stops it falling through? Should I put a layer of below the joists using plywood or O.S.B. to hold insulation in?). Then cover with DPM and then a playwood floor? Sound right so far? Any other tips e.g. treating timber as I go along?

Again thank you for the help, much appreciated.

One last thing (for now). How do I make sure the concrete is level with each strip? I note what you said about the pegs in the ground but unless I am being thick (could be!) this will only help me make sure the strip I am filling is level, how do I make each strip is level with each other, also would you recommend putting in hardcore first or just use concrete?

Thank you.

just before you start digging the depth is 150mm not 15" will reply to the rest tonight.

J

Jasonb said:

just before you start digging the depth is 150mm not 15" will reply to the rest tonight.

J

Click to expand...

Ah yes thank you.

To get all four strip level with each over you will need to level from the peg in one strip to a peg in the next. This can either be done with a waterlevel or use a long straightedge from strip to strip and rest your spirit level on this (may have to use a packer so it does not foul the soil in between.

Fill the strips with just concrete, if you use hardcore you will need to dig them deeper then still cover with the same amount of concrete.

Try yellow pages for steel stockholders, what part of london are you in? A good builders merchants should also keep a few lengths.

If you get the top of your blocks good and level/even then the DPC and plate(timber) can be laid straight onto, if they are a bit up & down then spread a layer of mortar ontop of the blocks, then DPC and then bed the plate down onto the DPCwhile the mortar is still wet. The plate can be held with plugs & screws say 100x6.0 into brown plugs about 500mm apart. The plate should be laid flat, ie 4" wide 2" high. Use treated timber for this.

150x50 (6x2) joists are just a fraction undersize if this were a house but they will be fine for this use, you can either buy treated timber which will be the best or coat it with wood preserver before fixing. They should be spaced at 400mm centers, though 16" will work better with 8x4ft boards

The insulation can either be stopped from dropping by fixing battens to the lower sides of each joist but thats a lot of work & timber. Probably easier to just run a few battens at rights angles to the joists and fixed to the joist bottoms.

Lay a polythene DPM over the joists then screw down your floor boarding which could be chipboard but I would go with plywood.

Jason

Brilliant, thank you Jason.

Ordered the water level, that should arrive today.

I've been trying to work out what size I should go for that will save as much time when it comes to the size timber you can obtain but I'm just thick and can't figure it out! I have a maximum width of 3.5 metres (this would leave a space between the sheds to get in and approx 16" back and left hand side for future maintenance). Length I think 10 metres is the max I would wish to go to).

Depending on best size width, how much concrete (bags of sand / cement) would I need to fill the strips length (= to width of build) x 300mm x 150mm?

When you wrote 16" (420mm) centres, do you mean the centre of one joist to the centre of the next joist is 16"? This maybe a very stupid question but assuming that is correct my first to second joist will be closer together than the others as I would do 16" from edge of first joist to centre of second joist then 16" centre from then on e.g. 1st Joist 0" (centre 1"), 2nd joist 16" centre (requiring only 13" between joists), 3rd joist 32" centre (requiring a 14" between joists). This continues until the last joist which would again be closer. This would then fit nicely with 8x4 as you mention? Have I got that correct?

Materials List (using Wickes):

BLOCKS: http://www.wickes.co.uk/invt/154040

CONCRETE:
Cement: ?
http://www.wickes.co.uk/Bagged-Cement/Mastercrete-Cement/invt/220023
http://www.wickes.co.uk/Bagged-Cement/Blue-Circle-Cement/invt/224661
Ballast: http://www.wickes.co.uk/Aggregate-Sand+Ballast/Ballast/invt/220082

INSULATION: http://www.wickes.co.uk/General-Constructional-Insulation/General-Purpose-Insulation/invt/161197
(1200 x 600, so is this the correct stuff as it would require cutting to fit 16" joists). Talking of joists and insulation, would it be better to board the underneath of the joists with O.S.B. or similar (saves battening to hold insulation in and prevents any little drafts, no?).

MORTAR (for blocks): http://www.wickes.co.uk/invt/154059
(Couldn't find the bagged stuff).

D.P.C.: http://www.wickes.co.uk/DPMs/Damp-Proof-Course/invt/152855

D.P.M.: http://www.wickes.co.uk/DPMs/Damp-Proofing-Membrane-1000-Gauge/invt/152859

TIMBER:
47x100mmx3.6m (plate): http://www.wickes.co.uk/Sawn-Treated-Timber/Sawn-Treated-Kiln-Dried-C16/invt/103619

Couldn't find 50x150 for the joists on Wickes. Where will I get them from? Rough price? Am I correct in assuming I just screw the joists together, galvanised screws? size?

O.S.B. (if used under insulation): http://www.wickes.co.uk/Underground-Drainage/Oriented-Strand-Board/invt/110024
Or could use 6mm plywood as price is very similar: http://www.wickes.co.uk/Sheet-Exterior-Plywood/Exterior-WBP-Plywood/invt/110117

PLYWOOD (floor): http://www.wickes.co.uk/Sheet-Exterior-Plywood/Exterior-WBP-Plywood/invt/110037

Anything missing? Tips on best size, cuts etc. would be very helpful.

Again thank you for the help.

All the best.
Michael.

I've been trying to work out what size I should go for that will save as much time when it comes to the size timber you can obtain but I'm just thick and can't figure it out! I have a maximum width of 3.5 metres (this would leave a space between the sheds to get in and approx 16" back and left hand side for future maintenance). Length I think 10 metres is the max I would wish to go to).

3.5 or 3.6 would be a good size with minimal waste

Depending on best size width, how much concrete (bags of sand / cement) would I need to fill the strips length (= to width of build) x 300mm x 150mm?

For each 3.6m strip you will need 260kg balast & 43kg cement using a 1:6 mix

When you wrote 16" (420mm) centres, do you mean the centre of one joist to the centre of the next joist is 16"? This maybe a very stupid question but assuming that is correct my first to second joist will be closer together than the others as I would do 16" from edge of first joist to centre of second joist then 16" centre from then on e.g. 1st Joist 0" (centre 1"), 2nd joist 16" centre (requiring only 13" between joists), 3rd joist 32" centre (requiring a 14" between joists). This continues until the last joist which would again be closer. This would then fit nicely with 8x4 as you mention? Have I got that correct?

In principal yes but 16" = 406mm, as long as your joints fall down the center of a joist you can allow a bit of leyway on the intermediates

Materials List (using Wickes):

BLOCKS: OK
CONCRETE:
Cement: OK
INSULATION:Not sure if its a rigid fibreglass batt, but I would go with polystyrene minimum, Celotex or Kingspan would be better

Talking of joists and insulation, would it be better to board the underneath of the joists with O.S.B. or similar (saves battening to hold insulation in and prevents any little drafts, no?). Battens probably cheaper and easier to fix, you only need them at 800-1000 spacing

MORTAR (for blocks): Will cost a lot, just get a few bags of building sand and mix 1:6 cement:sand

D.P.C.: OK
D.P.M.: OK
TIMBER:OK

Couldn't find 50x150 for the joists on Wickes. Where will I get them from? Rough price? Am I correct in assuming I just screw the joists together, galvanised screws? size?

Any decent timber merchants will have them, either nail or screw,

O.S.B. See above
PLYWOOD OK

Jason

Seriously, don't get your stuff from Wickes. They are ok for a lot of things, but insulation and timber are way overpriced, and the quality of the timber can be a bit slipshod too. Where are you in London? There's bound to be a builders merchant near you that will save you loads of money.

JB, you are saying to put the dpm over the timber, what about ventilation underneath? Personally I'd put the dpm over the ground, up the brickwork and under the wall dpc. and probably another on top too! Polystyrene sheets are cheap enough to be run under and between the joists.

I had suggested leaving the underside of the joists open, they will be off the ground, this will give adequate ventilation. DPM over top of joists and below ply floor, this should stop interstitual condensation forming within the insulation.

Jason

Hi Mike
consider this...is you go to a timber merchant or somewhere like Travis perkins...Go armed with a list of your potential requirements.
Also scan yellow pages for an independant as they are quite often cheaper !

For shed framing consider a product called CLS it comes in either ex 4 x 2 or ex 3 x 2 it finishes a bit smaller so bear that in mind it's all been machined and is a regular size and should also be cheaper than regular 3x2 & 4x2...price wise 3x2 cls @ about £1 m & 4 x 2 CLS @ £1.2 or cheaper

Jablite is a good product for insulation it comes in 8' x 4' sheets and you can get it in various thicknesses 25mm 50mm etc it cuts easy with a hand saw.

Thank you all for the advice, not sure what independent timber merchants are round here. I have a Travis Perkins nearby IIRC. I'm in Eltham, S.E. London.

CLS is also what Jason mentioned for the main frame, i'll post later today (Monday) for advice on the frame as I think we are basically there with the base now.. Thank you Jason. What is CLS and why is it better / cheaper?

Regarding ventilation, why is this important? Is it simply to help improve any damp issues?

Deluks you said you would put the DPM under across the ground, this is how I originally thought it out but wasn't sure how I would go about it. Thought it would look untidy coming up over the concrete and over the blocks or have I misunderstood what you are saying?

All the best.
Michael.

There's a place called Selco in Charlton. They are 'trade only' so you'll have to open an account, for which you'll need some letterheaded notepaper or a business card of some sort. You can knock these up on the computer or borrow a busi card from a tradesman pal. If you go in there and explain that you are a 'self builder' and indicate that you'll be spending a few hundred quid, they'll probably not be too fussed and just open an account in your name.

They also do free delivery over £100.

They are having a special throughout March on 6x2 which comes in all sorts of standard lengths so you won't have too many offcuts, and they are certainly cheaper than TP, whose prices seem to vary from trade and public.

Dpm can go over and under if you like, it will sit on the walls, under the wall dpc so won't hang over. You don't strictly need it though but make sure there are a couple of airbricks at either end of the blockwork base so the underside of the timber has airflow.

Thank you for the link. I've checked out Selco's website I was going to try making up a letterhead and sending it in for consideration but I think I will just phone them up tomorrow and see if there is a possibility of getting a cash account due to the amount I could be spending. If that fails then maybe I will try sending a letterhead in, if I decide to do that what should I put on the letterhead to make it look legitimate? I probably won't try it though, sad as it sounds I prefer to be straight with people. So failing Selco where else would be better than TP or Wickes?

Deluks, I'm not sure what you mean with the DPC. The way I have understood what Jason has wrote is that I should have 4 foundation strips the width of the area e.g. 10 metre length x 3m wide would have 4 strips of 3metres spaced every 10 metres. One course of blocks on each to raise the foundations above ground level, followed by DPC, then 4x2 plate, then joists + insulation, DPM, ply floor. Not sure I understand how you would run the DPM across the ground. I'm a little hard of hearing and find explaining things very slowly helps a lot .

Thank you.

All the best.
Michael.

Thank you for all the help thus far. I think we have the gist of what is required for the base and it is well noted. Now for the frame (maybe some one could write all this up afterwards as a little how to for future newbies).

Jason you said that I should use 38x89CLS. How high would you recommend? How far apart would you recommend having the uprights? 2 nogins per upright?

Insulation between the uprights (you mentioned fibreglass or rigid insulation but if possible could you point me the type you recommend, ty)? Cover the outside with 12mm plywood (could I use OSB instead?), you then mention breather paper but I can't find this, again could you point me to where I can find this? Then shiplap cladding e.g. http://www.wickes.co.uk/invt/120808

Inside cover studs / insulation with DPM (is this the same DPM as used under base e.g. http://www.wickes.co.uk/DPMs/Damp-Proofing-Membrane-1000-Gauge/invt/152859 ? Then cover with plasterboard http://www.wickes.co.uk/Plasterboard-95mm/Tapered-Edge-Plasterboard/invt/220207, tape & fill joints. Sound ok? I was originally going to do the inside with ply or OSB and then plasterboard over this, in your opinion is this simply a waste of time / money?

Should I be treating all timber as I go along or just coat the shiplap once it is all up?

The roof? Should I be thinking of putting the roof on before doing the internal walls (prior to placing insulation / DPM etc.) in case of rain etc. (as I doubt this is all going to be done in a day .

We move on to the roof next time, I'm thinking of a low pitched roof, plus how hard would putting in a skylight window be?

Again thank you for all the help. Hopefully once I get through all this I will be in a position to help others. I will take a few pics along the way. I hope to start once the builders have finished on my rear extension and the current weather improves.

All the best.
Michael.