How to approach a doorway for a workshop on a brick soleplate

[Chris Suffolk]

I am planning a workshop that this time I might actually follow through with. There will be a concrete slab, roughly 3.6mx3.6m. I'll be laying a single course of heavy/dense concrete blocks to give me a height of 125mm (slightly more after mortar) upon which I will build the timber frame. Standard stuff. Except I will not be using a wooden floor. I'm a big guy in all dimensions and between me and heavy machines I just don't want to deal with a spongy wooden floor. Instead I will just use the concrete slab as the floor. Again that's not unusual but the issue is the course of blocks. My intention was to have them all the way around but then I'd have to step over 125+mm of brick to get in and out of the workshop which is just not ideal when it comes to moving heavy things in and out. It also just looks naff for when I come to sell the house.

The only alternative is to have a gap in the brick course for the door frame (or a much lower lip just to prevent water running in, maybe 25mm or so). I intend to use a PVC double door with PVC frame so I am not worried about the doors or the frame wicking moisture up or getting rotten. Is that a sensible plan?

 

[macca]

Do you need a brick course at all? are the edges of your slab going to be above grade? if so and you have a decent clearence I would do away with the brick course and lay the plate for your wall on dpc and bolt it down into the slab itself, lap the dpc up the back of the wall and down the face of the slab externally with your exterior cladding lapping down over this (manufacturers etc would want 150mm clearence from ground but it up to you ultimately) this will be much simpler and stronger than a course of block which to be quite frank is pointless as you have no cavity to form a tray you will just have an issue with moisture ingress.
Real belt and comfortable braces would be to have a course of block below your stud wall (on edge not flat) and have 150mm pir with a ~70mm screed. The best home builders ive worked with actually cast a concrete curb on the inner leaf of cavity instead of a course of dolly blocks as the blocks are more vulnerable but thats probably above the call of duty here.
again I would sit any timber plate upon a dpc where it contacts masonry.

 

[HappyHacker]

The better wooden stables recommend that the sole plate be installed on a course of engineering bricks with a DPC membrane on top. The stables do usually have damp materials on the floor inside though. The stable doors do not have cill. A PVC cill will solve the problem and I dont think mounting it on top of something else will add any benefit.

 

[ChaiLatte]

Instead I will just use the concrete slab as the floor.

Just an observation. That will be cold and hard on your feet. 25mm of insulation and 18mm chipboard will make a much nicer working environment. For heavy fixed machinery, a plinth can be made before fitting the floor.

...to prevent water running in

A possibility is to put an Aco drain along the door threshold on the outside.

 

[Chris Suffolk]

Do you need a brick course at all? are the edges of your slab going to be above grade? if so and you have a decent clearence I would do away with the brick course and lay the plate for your wall on dpc and bolt it down into the slab itself, lap the dpc up the back of the wall and down the face of the slab externally with your exterior cladding lapping down over this (manufacturers etc would want 150mm clearence from ground but it up to you ultimately) this will be much simpler and stronger than a course of block which to be quite frank is pointless as you have no cavity to form a tray you will just have an issue with moisture ingress.
Real belt and comfortable braces would be to have a course of block below your stud wall (on edge not flat) and have 150mm pir with a ~70mm screed. The best home builders ive worked with actually cast a concrete curb on the inner leaf of cavity instead of a course of dolly blocks as the blocks are more vulnerable but thats probably above the call of duty here.
again I would sit any timber plate upon a dpc where it contacts masonry.

If I understand correctly you're saying that all of need to do is lay a strip of dpc then lay a wooden plate onto the dpc? The concrete slab will be around 80-100mm above the nearest surface. I do want to bolt the plate down but that would mean puncturing the dpc, I wasn't too worried about that if I was using a course of blocks because the dpc itself would be 125mm above the concrete slab but not sure how I feel about it when it's directly on the slab. I was going to use something like the epoxy/chemical anchors so maybe that would help seal any small breach and then the pressure if the nuts being tightened would mechanically seal it but I'm not sure.

 

[Chris Suffolk]

Just an observation. That will be cold and hard on your feet. 25mm of insulation and 18mm chipboard will make a much nicer working environment. For heavy fixed machinery, a plinth can be made before fitting the floor.



A possibility is to put an Aco drain along the door threshold on the outside.

I'll be alright, I'm hard! Thing is I'm 193cm tall so I quite literally don't have a lot of headroom when taking into account the permitted development max height (when you consider that internal joists, cladding, light fixtures etc take up a good 20cm anyway). Adding a floor just reduces the height even more. If it gets really bad then I can add a floating floor later but to be honest if it's cold I just wear boots. Good point about a drain outside the door though, might look at that option.

 

[ChaiLatte]

...I do want to bolt the plate down but that would mean puncturing the dpc

If you are doing it yourself, you can afford to take the care that a professional might not have time for.

Install the anchor bolts first. Splodge some suitable (e.g roof and gutter) sealant around them then push the DPC over the top. Seal around the top of the DPC where it is penetrated by the bolt as well.

 

[Chris Suffolk]

If you are doing it yourself, you can afford to take the care that a professional might not have time for.

Install the anchor bolts first. Splodge some suitable (e.g roof and gutter) sealant around them then push the DPC over the top. Seal around the top of the DPC where it is penetrated by the bolt as well.

Aye that was roughly my idea although I didn't think of using actual proper sealant. The cladding outside will extend over the edge of the slab and presumably I'll need to leave a gap ensuring that the cladding never contacts the side of the slab otherwise it'll just bypass the dpc? Any other considerations there? Doesn't seem worth using treated timber because if it gets wet the issue isn't rot in the soleplate it's the fact that moisture will be passed up to the untreated sections anyway.

 

[johnnyb]

course of block then course of brick by the doorway. aco drain all around perimeter or at least the door.

 

[Chris Suffolk]

course of block then course of brick by the doorway. aco drain all around perimeter or at least the door.

A layer of brick is still quite a nobstacle for heavy things, do you think I can go any lower in height or is a brick about the limit?

 

[johnnyb]

as long as your drains are perfect then a smaller step would be fine. but some ramp could work. the whole slab could be raised.

 

[Chris Suffolk]

as long as your drains are perfect then a smaller step would be fine. but some ramp could work. the whole slab could be raised.

Cheers, thinking about it the slab in that area will actually be raised anyway so I may use a strip of treated timber under the doorframe just to give it something to rest on (as it will be a PVC unit with all four sides). If that bit of timber gets rotten eventually I can replace it and it will only be in contact with the PVC and the concrete blocks either side so shouldn't be able to wick moisture anywhere

 

[macca]

At the end of the day any masonry is not water proof, modern masonry walls are only impenetrable by moisture by employing a specific series of dpc's and ventilation to keep moisture away from an isolated inner skin of masonry. the only way you are going to keep a single layer of masonry IE a course of block and your foundation dry is to shield it from any moisture.
if you will only have a few inches above ground maybe consider using a course of block after all. Hopefully you have enough dpm sticking out around your slab to bring it back up and cover the edges of your slab. Lay a dpc as I suggested before, under wall plate, lap this down over the block and the top of the dpm beneath your concrete slab this should keep any moisture from passing from the ground into any concrete or blocks, at the doorway you do not need any course of block, end the blocks and timber plate either side of the opening with dpc lapping down over the ends.

If you are worried about water passing under the cill get a lead tray welder by a local roofer. The blocks are only really there to lift the bottom of your timber and any cladding up above any splashed water.

You should really batten and counter batten behind any cladding to allow airflow and mesh opening to prevent bugs the overhang from doing so will also enhance your protection from moisture, drainage is always a good idea but easily retrofitted if time or budget are a constraint.

In regards to piercing the dpm and sealing, yes you are right its good practise but in this scenario, if there is moisture either side of your dpm at that point, it is already on a path to the interior of the wall. below is concrete floor of the workshop and above is the timber plate of your wall

 

[TomGW]

I don’t know why you are considering any brick/block through the doorway. I’ve used a standard uPVC door & frame and cut the slab to reduce the cill height to a minimum - obviously you can reduce it to zero if the door opens out.
On my daughter’s garden room I used a similar block base and faced the block and exposed edge of the concrete with roofing slate stuck to the face of the block/conc with Tech7. I used 100mm strips of dpc vertically behind the butt joints of the slate to minimise the possibility of damp penetration. The slate totally bridges the joint between the slab and the bottom of the row of blocks and also provides a rain protection to the exposed edge of the concrete base.
The slate etc was done before starting to construct the timber, so the dpc on top of the block extends over the edge and is bent down by the cladding that extends down by about 40-50mm.
Four years on its totally dry and the slate base looks really classy with the cladding finished in a grey/green wood finish.

 

[DeanH]

Could you not just butt your block work up to either side of the door? You could lap your DPC down and under the frame if you were worried about the detailing.

 

[Tuco]

I’ve done a similar thing with 50mm celotex then a power floated screed on top and it’s great. Like standing on a rock and great for sweeping.