Damp course / foundation for a wooden building

[ME]

I am going to get a timber building made at the bottom of the garden. My mate is an chippy and is going to build it hopefully.

 

At the moment I have a 6 metre x 4 metre concrete pad that is 6 inches deep running to 15 inches at it's deepest point. (the ground slopes away) It has steel reinforcing running through it.

 

What is the best way to build up from there? Are we talking a few courses of bricks and a DPC? or DPC direct on the slab and build up from the ground?

 

I want the building to look all timber so would have to clad over if bricks are involved.

 

What say you PW?

 

 

 

 

[Kes]

Wood will rot whenever its in the zone where splashing water will reach.

I would build a 9" brick foundation and use a 'U' shaped membrane from top of bricks to inside the building and back between the brick and the concrete, this if you use a single skin porous brick . I would use standard dpc material and run a piece of double thickness visguene? under both or if it will be regularly wet, go for a hard glazed engineering brick cavity construction with 'wallplate'. I would NOT overclad it and if you choose a blue engineering brick it could/would look rather swish.

All the best.

[sako751sg]

What's the ground levelaround the pad?if its near level I would do a base course of bricks/blocks and then dpc off of this.

[Rupert]

and get some airbricks in to vent the void underneath.

[ME]

It is at the same level as the surrounding ground.

[sako751sg]

Keep it up a good bit then.I personally would have at least 3 course of brick, then your dpc and as stated I wouldn't allow the timber to go right to ground level as the damp and splash would make it look minging and also rot over time.If you use facing brick as your external skin then stop the timber well up you will still have a nice finish.

[Yellow Bear]

Wood will rot whenever its in the zone where splashing water will reach.

I would build a 9" brick foundation and use a 'U' shaped membrane from top of bricks to inside the building and back between the brick and the concrete, this if you use a single skin porous brick . I would use standard dpc material and run a piece of double thickness visguene? under both or if it will be regularly wet, go for a hard glazed engineering brick cavity construction with 'wallplate'. I would NOT overclad it and if you choose a blue engineering brick it could/would look rather swish.

All the best.

Have done this with blue eng. bricks and yes it does look swish

[bruno22rf]

We have a 5mx4m log cabin at the end of our garden that my daughter lives in (and visitors use) and it simply stands on a concrete base with treated timber batons (approx. 4"x4") underneath spaced about 1/2 metre apart. These are eventually going to rot but the building can be lifted enough to simply slide a replacement baton underneath when the time comes. Inside the cabin we have a damp proof membrane on the floor with laminate on top. Its been there over 2 years and has been totally dry and even insect free.

[Jega]

Three courses of engineering bricks ,sufficient air bricks to allow adequate through flow of ventilation ,damp proof course. What is far more important is to really get to grips with the timber protection aspect of the build, it is absolutely imperative to get plenty of preservative on to ALL the timbers.

[ack-ack]

What stone cladding you going for geezer?

[pegleg31]

Lay a course of blocks on a damp course then blind the original base with a inch of sand and cover with a damp proof membrane. Depending what the building is goinig to be used for you could either insulate the floor and concrete or just concrete to the top of the blocks. Once it's done fit the stud work of the building onto your raised pad placing dpc onto it first. Cover the.stud work with OSB or ply and cover this with a breathable membrane and fix tile latts over, either vertically or horizontal depending which way you want your finished cladding to go. Doing it this way will cover the block work and make it look all timber and it will also allow air to flow to help stop the building from rotting.

 

Pegleg

[Scully]

We used old railway sleepers bolted down on to concrete pad for one we did,wall-plate flush with external edge of sleepers with waterproff membrane(black plastic sheeting,couldn't find any DPC wide enough) lapped up behind from inside edge to prevent tracking,then after timber frame (Swelite Masonite I-beams) was up on 400 centres,clad with vertically double lapped Siberian Larch onto horizontal tanalised roof battens.The bottom edge of Larch boards shoots past top edge of sleeper to about half depth of sleeper so it can drip dry and air dry.Air-flow is created by gaps between sleepers .Straps from sleepers to studs prevents wind picking it up and moving it into neighbours garden.

Floor built wih 150mm Masonite beams spanned across sleepers.The roof is simplified by making it mono pitch and all internals can then be sheeted with OSB and can then even be cored and insulated with Warmcel if you want;stick in a wood burner and you'll be as snug as a bug in a rug.

[Gimlet]

Any DPC course should always be a minimum of 6" (two brick courses) above surrounding ground level to prevent rain splash. I'd lay three courses of brick, DPC on top, then the timber frame. If you're using something like feather edge cladding allow the bottom edge of the first piece to extend an inch below damp without touching the brick. That will prevent water getting under the DPC by capillary action. Make sure your brick dwarf wall is perfectly square. Not half an inch out but absolutely spot on. Your chippy's job will be much easier, quicker and cheaper.

Are you planning to use the concrete slab as your finished floor surface? If you are it needs to be lined and, if you want to use the building rather than just store things in it, insulated. A single leaf of brick work will be damp on the inside, so you'll either need a cavity dwarf wall which isn't practical with a single leaf timber frame on top, or you need to raise the floor to DPC level incorporating insulation and Damp proof membrane while you're at it. If you want to float a timber floor on the brickwork above the slab, then as Rupert says, you must build airbricks into the brickwork (two on each long side) or your floor timbers will get dry rot.

Unfortunately, if the existing concrete is just an unlined, uninsulated slab laid directly onto hardcore it isn't much use as a floor in a dry habitable building as it is. Its essentially a foundation. You'll need to build it up or float across it in timber.