Workshop build pre build

[DennisCA]

To be more precise, it's EPS (Expanded Polystyrene) that was used here.

Here's an old image I found from before the slab was cast in my house, that's hydronic heating PEX hoses and rebar, standing on top a thick layer of EPS foam sheets. In the center where there is more rebar and less EPS is where the foundation was reinforced for a 1.2 ton mass heating wood stove:
https://c1.staticflickr.com/3/2841/1103 ... 9633_b.jpg

Underneath the foam there is packed & vibrated gravel.

 

[technium]

Thanks Dennis, so the purpose of the foam is just for insulation then. Does the foam have to fill the whole void or does it just need to cover the concrete? I mean if between the wood floor and concrete is 100mm gap can I use 50mm foam / insulation or do I have to fill the whole 100mm void with foam? im thinking from a cost perspective.

Also I think I might try and cost a self build, so for the size I want what do you guys recon purely for the frame work and roof beams? 4 x2's or 3x2's or what? I can then try and work out how many I might need and price up that aspect first.

thanks again

Colin

 

[DennisCA]

Hmmm, I think you might have gotten things mixed around, the EPS foam goes under the concrete plate and insulated the concrete from the ground itself. In the picture there the concrete was not yet cast in place.

 

[cammy9r]

Hi, good bit of confusion here I think. Technium I believe is having a wooden floor to the workshop not concrete. There will be no need to put EPS in the concrete base. I doubt a 6" pour over both existing concrete and sub base will crack, however rebar is a wise choice.
Have a look at this website for a bit more clarity on concrete bases : http://www.pavingexpert.com/concrete.htm
The website is cluttered with huge amounts of info and has served me well over the years.
If you have easy access to all sides of workshop then leave cladding until the frame is wrapped with breather membrane. Google breather membrane for more info on its uses. I use Permavent Eco as it is reasonably priced and see no need for super stuff for a large hut. For frame and roof you can use 4x2 cls, usually works out close to £1 +vat per meter for 38mm x 89mm or £1.30 +vat for the 45mmx95mm. The cladding will likely work out to be the most expensive part of the build.
The frame can be built on 600mm centres to keep cost down and will be plenty strong once sheathed internally with ply or osb ~9mm thick.

 

[technium]

Thanks Cammy.

You are right, it would be a concrete base to support the workshop with a wood floor. Im still debating on building myself so will consider what you have said but at the moment im still edging towards the prebuilt setup.

thanks again.

 

[RobinBHM]

Hi Colin,
Im in the process of building a 5.4m x 2.7m shed, so virtually the same size as yours.

The huge advantage of building your own, is that it is possible to construct in the same way as a timber frame house. Ive done this by starting with 4 x 2 section studwork, doubling up at the corners. I made in sections about 1220mm wide and screwed together. The strength comes from a plate at bottom and one on top.

I then clad the outside with 18mm osb3, which was then covered in tyvek housewrap. My next job is to fit 2x 1 tile battens vertically all round to create an air gap before fixing on the the featheredge cladding. It is the tyvek membrane and air gap, that makes a home built workshop so much better than a ready made shed. The mambrane makes the structure really air tight and nice and dry inside, whilst the air gap allows the cladding to be ventilated behind and dry out quickly giving it a longer life.

 

[technium]

ok guys im getting to the point where I need to think about the base now for the workshop. What are your thoughts on either a full concrete slab as the base with a wood frame and floor sat on the concrete or having just blocks cemented in place and then the shed frame sitting on those? I expect the later option would be cheaper but is there a reason to choose one or the other?

thanks

 

[RogerS]

I'm sure you've seen Steve Maskery's warehouse (sorry, workshop :wink: ) thread. But you might have missed several WIPs on workshops/sheds being built over on thewoodhaven2.co.uk such as here and here.

 

[Fitzroy]

Only real benefit I could see in a wood frame sat on a concrete slab is that you could have the wood frame made of smaller timber say 2x2s as opposed to a wooded frame on concrete blocks. My frame is made of 6x2s with a max span of 2m between some blocks, with an 18mm OSB floor it feels good and solid. Downside of using such a system is you would be limited to the insulation you could get in the floor, it that's something you plan to do.

A pal of mine recently built a shed with an insulated concrete slab for the floor and it was back breaking work digging, filling compacting, concreteing etc etc, and fairly costly with the cost of sub base, insulation boards, membranes and concrete. I thought the suspended floor on concrete blocks for my build would be easier and cheaper but to be honest it was not, it was still a back breaking task and probs cost 20% less. If I were to be doing it again and did not have the planning constraints I have then I would go for an insulated concrete slab.

F.

 

[technium]

Thanks guys.

I thought maybe the blocks route would be alot cheaper but obviously not then. Getting to the stage where I need to decide, problem is I cant decide!

 

[technium]

Hi guys

I thought I would update this thread with whats been happening.

I have now dug out 4 cubic meters of soil from the old place of the old wooden shed which left me a level base. As the base next to where the wooden shed was is already 6" thick concrete (10'x8') then I have dug down 4" and filled with Type 1 Sub Base and compacted it down to within an inch of its life.

I have purchased some Visqueen dpm to cover the whole area under the new concrete slab. A week on Saturday I have planned for some help from friends to fill the whole area 11' x 19' with 6" cement slab which will also have rebar in it to try to minimise cracking between the area that already has cement base and the newly created compracted area.

As the slab will be bigger than the shed I plan to put some drainage in to minimise splashback and also to hopefully stop water sitting under the shed.

Think thats all for now.

 

[technium]

Ok today and yesterday me and a couple of mates laid the cement slab 5" thick and with rebar within it to keep it strong. I have dpm under the slab but when my new shed arrives, should I put another layer of dpm on top of the slab to protect the wood floor of the shed?

Heres a couple of pics of the slab all done and ready. Last pic shows damn cat paw prints that I had to fill :evil:

 

[technium]

I have dpm under the slab but when my new shed arrives, should I put another layer of dpm on top of the slab to protect the wood floor of the shed?

Anyone? :?

 

[Fitzroy]

If the shed sits in the pad and rain can get between the pad and the shed base the you need to do something to stop the wood taking up the moisture. If the pad is elevated and will be the shed floor such that the shed cladding will keep water off of the pad then no. Similarly if the pad is raised and you plan to extend then shed cladding to below the level of the pad such that it cannot get wet then you could forgo the dpm, although I would still use pieces between the pad and the wooden base.

 

[technium]

Thanks

The cement slab is 5" above ground level with a trench all around it. The slab is the same size as the shed will be so the hope is that rain will fall down the cladding and into the trench and not on the cement slab. The two vertical trenches you see in the photo are Arco drain which will be filled with pebbles and hopefully soak away any way that does make its way onto the cement slab.

 

[technium]

Hi guys

Ive noticed that the dpm that surrounds the slab keeps laying flat so when it rains etc it fills up between slab and dpm so I assume that means water is then getting underneath the slab and the dpm is then pointless. Is there a way to seal this properly? I read on a foreign forum about liquid Rubber to paint the side of the slab and dpm and stick it to itself but is there something similar in the UK or do you guys have any ideas?

Also at work I have been offered lots of 1" thick plastic like bricks that I can use to sit the shed bearers on which will keep the bearers off the floor but will I need to be worried about vermin getting underneath and if so then what do I need to use to stop that?

Finally I saw on another thread that someone suggested using a dpm skirt all around the shed which is stapled to the bearers and makes any water run off the shed onto the dpm skirt and then away from the cement slab so any thoughts on that idea?

thanks

Colin

 

[technium]

Anyone have any ideas?

 

[Fitzroy]

Colin,

I think you've reached the point that many of us get to in our shed builds, that you're into a bit of a unique situation, and you'll need to make a decision based on more generic info. If you look at the sticky build-a-shed-mike-s-way-t39389.html, there are a few pictures of how to do the slab and where the dpm sits in the overall scheme. Not sure it will totally answer your questions but it may help.

Also if you search google for 'concrete slab dpm' and look at images there a a bunch ie. "http://www.greenspec.co.uk/images/web/refurb/groundfloor/above-slab.png" that tend to show the dpm being brought up the side of the slab and then forming the dpc (damp proof course) in the brick work. All of these show a similar aspect that there is some form of protection to ensure the rain does not get inside the dpm. If i were you i'd batten the dpm against the concrete slab using treated roof battens, then extend some kind of flashing (either more dpm or boarding of somekind) from the shed over the top of the dpm.

Again, if you search google for 'flashing concrete slab' and look at images there are a bunch that may give you some ideas about how to resolve your situation.

Cheers

Fitz.

 

[DennisCA]

Concrete sucks up and releases moisture, though if it's in an heated enviroment it'll dry out over years. But in construction and the outwards facing walls, it was very important to get a barrier between the concrete and lower wooden portion of the walls because that concrete will never dry out:
https://c2.staticflickr.com/8/7383/1076 ... 275d_b.jpg

Hard to say with an interior floor, if it's in contact with the outside and moisture can migrate like that then perhaps a barrier is better...

I painted my workshop floor instead, albeit 2 years after it was done.

 

[technium]

Thanks,

Theres a picture here http://www.pavingexpert.com/images/conc ... geBase.gif which seems to show what I am talking about and that has the gaps around back filled so maybe thats the solution although I still kind of like the idea of sticking the dpm to the base either with the rubber glue stuff (would roof bitumen work?) or Fitroys batten idea.

I think the lower portion of the walls should be ok as that will be sat on the plastic bricks and they inturn will be sat on the concrete slab so no part of the shed will be in contact with the base.

Just so you know the shed will have a wooden floor sat on 4 x 2 treated bearers so I wont be using the concrete slab other than to support the whole structure.

thanks

Colin