Yet another shedshop Mike's way. Ish

[MikeJhn]

Turned up and sealed against the concrete, or paved over with a fall away from the building, "NB", it's always a problem with a raft slab without a separate strip footing for the brickwork to enable the DPM to be turned up the wall internally.

NB we then have the problem of ensuring the paving does not provide a path for water to penetrate under the slab, flexible joint between the paving and concrete, a decent overhang of the roof and guttering will help.

 

[Woody Alan]

I may be wrong and happy to be corrected or open discussion, but I thought Mikes advice re the damp membrane under the concrete was to cut it away and expose the edges of the slab. The theory being the slab retains a level of moisture for a long time and its only egress will be by the edges, yes it will get a little damp when rainy but will dry out as well the same as a driveway. As long as there is a membrane between slab and structure then all will be well.

 

[Adam W.]

Er, well, that would possibly let moisture in through the edge of the slab.

Normal construction seals the slab from any moisture by using a dpm lapped with a dpc. If it was mine, I'd just seal the slab and create a dpc at the same time by rolling a membrane over the top of the slab and lap under the dpc at the bricks. But it's a cack handed way of doing it just to avoid digging a shallow strip foundation and doing it the 'normal' way and it also requires screed to protect the dpm.

 

[aphillippe]

Yesterday:

brickwork done. Not pretty but should be good enough.

this evening, sole plates cut…

 

[aphillippe]

Had a quote from my local builders merchants for the 2x4s for the roof trusses. I don’t need much of it (I chose 3x2 for most of the frame) but I couldn’t believe £9.60 per metre, ex. VAT. Obviously timber prices are high at the moment but not that high surely? What’s it like in the UK at the moment?

I rang around and found cheaper (£6.50 for 2.4m lengths from magnet trade counter) so will be picking them up later today.

 

[MikeJhn]

Hmm truss's that brings back memories.

 

[aphillippe]

Interesting. I'd love to get in to truss design to really maximise space as in your example. Playing it safe for the shed

 

[Spectric]

Don't stress about the slab, the shed weighs nothing.

But what about the contents, the mass of the shed will be spread across the slab but the contents will be point loads.

You should have enough CBs in the consumer unit with the RCD to supply the ring, the lights and as many 16A supplies as necessary plus one extra for the future. I found a 40A supply cable to be enough for my needs.

Don't forget the regs and your means of earthing, and don't be historical, use radials like in any industrial enviroment because rings are old hat. You will always be safer getting an electrician to ensure your installation is safe, there is no such thing as a 40A supply cable. In basic terms you determine the absolute max current that will be drawn and then find the right size cable that can supply that current over the length of the run whilst maintaining a voltage drop within 5% of the supply.

 

[aphillippe]

But what about the contents, the mass of the shed will be spread across the slab but the contents will be point loads.


Don't forget the regs and your means of earthing, and don't be historical, use radials like in any industrial enviroment because rings are old hat. You will always be safer getting an electrician to ensure your installation is safe, there is no such thing as a 40A supply cable. In basic terms you determine the absolute max current that will be drawn and then find the right size cable that can supply that current over the length of the run whilst maintaining a voltage drop within 5% of the supply.

I’m getting a sparky in to do all the electrics. I can wire a plug but not much more. Happy to bear the cost to keep things safe

 

[Molynoox]

Nice fusion model
I know you are going for thinner wood to save cost but your headers look quite undersized to me. Don't know what your roof covering is and hence if it's heavy or not but you don't want your doors and windows getting compressed from above as they won't open properly.
Interesting build thread, enjoying the progress
Martin

 

[aphillippe]

Nice fusion model
I know you are going for thinner wood to save cost but your headers look quite undersized to me. Don't know what your roof covering is and hence if it's heavy or not but you don't want your doors and windows getting compressed from above as they won't open properly.
Interesting build thread, enjoying the progress
Martin

OSB, membrane and then probably onduline (or equivalent) bituminise sheeting. Or maybe EDPM. Haven’t decided. Onduline is available locally and will be about £350 to cover the roof. EPDM looks better functionally but is a new material to me and not available locally. Shipping to a small island in the middle of a big puddle can be tricky sometimes.

Re the headers, it’s worrying me too. I got my window the other day. It’s from the window company’s ’graveyard’ to keep costs down. Pretty much the only thing they had at close to the right size. 1800 wide. So the above configuration for headers is not going to work. I have some 4x4 fence posts sitting around that would be better. Between that and the (two) top plates, there would be very little deflection. And we don’t exactly get a lot of snow down here.

 

[aphillippe]

Progress through the week and yesterday…

I didn’t get any photos but through the week I mortared in the sole plates and DPC. Strapped down the soleplates to the brick (I was going to cast the straps into the concrete but didn’t really have time during the pour).

Starting to build the frame…


Side and back frames done…



Got a nice bonus this year so treated myself…

This thing is not light. Not in any way practical for a job site. But boy can it chop wood. 5-6 studs at a time makes the process go a bit quicker.


Lessons learned…

Measure twice cut once is a thing for a reason. But don’t just measure twice. Think about things a bit more before cutting. I failed to realise that the back frames were intended to sit under the gable end top plates and cut them to the same height and didn’t realise until they were all done and ready to be installed. Doh. Still at least they were long and not short.

Load bearing pieces should always sit on a supporting stud, not be screwed into the side of a stud. I cocked up the apex of the gables. Should have had the ‘rafter’ piece sitting on the king post rather than screwed to it. Again, think first. It was ‘proper’ in the plan so no idea why I did it wrong. I’m thinking that, since that whole face will be supported with OSB it will still be fine.

Today’s job will be to finish the front wall and do the roof trusses. And any time left will be starting on the roof.

 

[Adam W.]

Snip/
But what about the contents, the mass of the shed will be spread across the slab but the contents will be point loads.
/snip

It's too late, he's already poured the slab.

Anyway, the Kingspan and panel floor will distribute the load. The only other solution is a steel reinforced screed on top, but it looks like that's unlikely to happen.

I've got my Vicmarc directly on an un-reinforced limecrete floor without any issues, and that weighs around the 400kg mark.

Plus, you don't seem to have lapped the DPM and DPC. Is there a reason for that ?

 

[Molynoox]

OSB, membrane and then probably onduline (or equivalent) bituminise sheeting. Or maybe EDPM. Haven’t decided. Onduline is available locally and will be about £350 to cover the roof. EPDM looks better functionally but is a new material to me and not available locally. Shipping to a small island in the middle of a big puddle can be tricky sometimes.

Re the headers, it’s worrying me too. I got my window the other day. It’s from the window company’s ’graveyard’ to keep costs down. Pretty much the only thing they had at close to the right size. 1800 wide. So the above configuration for headers is not going to work. I have some 4x4 fence posts sitting around that would be better. Between that and the (two) top plates, there would be very little deflection. And we don’t exactly get a lot of snow down here.

It's worth trying to sort the headers at this stage. You are only looking at under £50 of wood to ensure the windows and doors work properly.
Nice saw, I have the smaller version, quite impressed with mine, no complaints anyway.

Martin

 

[Ollie78]

Looks good so far, I wouldn't worry about the steel in the slab ( too late anyway ) my Dad did a garage with the same method as yours at least 15 years ago and its still fine.

Personally I would not bother with the diagonals on the frame. Just put breathable membrane on straight away to protect the OSB.

For the roof I would seriously consider trapezoidal metal roofing. It is superior to
onduline (by a lot ! I think onduline is crap) and felt and probably even EPDM.
It is easy to fit and pretty much maintenance free.
Don't skimp on guttering either I like the metal stuff there as well.

Ollie

 

[macca]

+1 for turning your visqueen up around your slab and up the back side of your brick course, not really the conventional way but between your bricks and slab you have circa 200mm of porous masonry at the base of your walls, alas the ship has sailed just ensure your cladding has enough over hang to deflect any rain away from the area. I can see in your images that you slab is below grade and the excess DPM at this point is holding water against the slab, good for the initial cure but you need to dig away the ground immediately surrounding the pad and get this level down.

RE correcting your wall line, really no issue again this ship seems to have sailed at this point but you should be battening off your osb outer skin to create airflow behind your cladding so pull a straight line for you plates that can be extended with said batten to overhang your lower courses of masonry. if you aren't battening your OSB push your timber out to the outer edge of the bricks and batten your internal wall, you can vapour barrier continuously around your inner stud work prior to battening and create a service void behind your internal sheet goods and add extra grounds for loading points on your wall that you may need a fix between studs and have inevitably not considered at the rough framing stage.

don't worry too much about your OSB it will need a breather membrane that will keep the rain off but honestly you'd be surprised how well it holds up to rain when its upright on a wall regardless, if you don't get osb for a while brace internally with some cheap battens, you should be using diagonal braces to plumb you walls anyway and these prevent racking, you can also use a batten across the corners of your walls internally to straighten any top plates that aren't quite right, most affective would be top plate down to adjacent floor plate but you run out of space quite quick on a small footprint like this.

lastly id look at alternatives to onduline, if edpm is within budget then ok but box profile metal sheets would be my choice, celotex under this and long fixing for the roof sheets through insulation into the purlins ties it al together nicely and support the sheets really well which can reduce the amount of timber needed for your roof on a low pitch.

reinforcing mess has become ridiculously expensive. yes you should have it in the slab in an ideal world, in reality will it crack? I doubt it, I just dug up 30 sqm of concrete 100mm thick no hardcore underneath and areas undermined by pests, not a single crack in it until i got involved always better to be safe than sorry, its a standard for a reason and you hardly want to have to replace a slab on this kind of construction after a couple of years but I would put good money on this being just fine.

 

[aphillippe]

Plus, you don't seem to have lapped the DPM and DPC. Is there a reason for that ?

I'm following Mike's design. I'm planning on cutting the DPM at ground level and sealing it to the concrete. I couldn't really see any other way of finishing the DPM other than take it all the way up and over the outside of the bricks and under the DPC, which then exposes the DPM to UV. This is the problem with floating slabs.

 

[aphillippe]

Personally I would not bother with the diagonals on the frame. Just put breathable membrane on straight away to protect the OSB.

I ended up skipping the diagonals 'in frame' and put temporary diagonals on the outside. Should have done on the inside but I was building the frames outside facing up, so was easier. I can go round and transfer them one by one to the inside before I put the membrane on. I don't know how long it will be between framing and getting it water tight (I'm only able to work on it at weekends) so want to keep as much OSB out the picture as I can until it's watertight

 

[aphillippe]

For the roof I would seriously consider trapezoidal metal roofing. It is superior to
onduline (by a lot ! I think onduline is rubbish) and felt and probably even EPDM.

My problem is that there is one main builders merchant in Guernsey that has the island over a barrel. Their prices are inflated through the roof. There are many smaller merchants who deal with the common items, 2x4s, OSB etc at reasonable prices. And a small B and Q. Shipping smaller loads of materials is very inefficient price wise. Shipping larger pallets gets a bit more reasonable but I don't have the space to store that much stuff. So I'm having to go round all the smaller merchants and, in order to stick to budget, I'm mostly limited to what they stock.

So, in this example, BandQ sell the onduline knock off stuff. I used it on my last shed and it was ok. Probably not 25 years ok, but good enough. And cheap, £380 I think. I did a ring around on the metal roof sheets and only the main builders merchant sells it. They wanted £800 ish.

Because of this issue (and my relatively tight budget) I'm having to make all sorts of compromises on materials and design. I'm confident I'll come out of the end of it with a reasonable workshop, but it's not going to be as nice as if I lived in the UK and had access to the range of merchants you guys have.

Anyway, I'll stop moaning now and say thanks for the suggestion.

 

[aphillippe]

ensure your cladding has enough over hang to deflect any rain away from the area. I can see in your images that you slab is below grade and the excess DPM at this point is holding water against the slab, good for the initial cure but you need to dig away the ground immediately surrounding the pad and get this level down.

I'm going to have about about a 25/30mm overhang between the outer edge of the brick and the outer edge of the cladding, depending on which cladding I end up with. Does that sound enough?

The bottom of the slab is below grade, the top of the slab is between 5 and 10 cm above. I'm planning on cutting the DPM off at ground level then backfilling it with gravel to 1 provide a bit of a soakaway and 2 avoid as much splashback onto the bricks as I can