Workshop Build - advise on water ingress

[tohowe]

Hello everyone!

I've lurked on this forum for some years and in summary have followed the "Mike's Workshop Build (Extension & slates)" design/build principles as laid out there. Mike - Just after some advice/clarification on a water ingress problem if I could kindly pick your brains please?

Bit of a long one....sorry!

A bit of background...3 years ago I discovered my shed (sat directly on concrete base. There since we moved in I will add!) was severely rotting. I knew I needed something bigger to store all my tools etc, balking at the cost of the prefab jobs and being somewhat practically inclined I stumbled on Mike G's thread mentioned above and decided I was going to build my own workshop, so thanks for the inspiration Mike!

So 3 years after having removed the rotting mess, the greenhouse converted into a "greenshed" storing lawnmower etc, bikes stacked up in the side of my office I am pleased to say that I am on the home straight with a 7m x 3m apex workshop.

I have followed the design per the aforementioned thread barring a few differences one being the roof construction which I made up of plywood underside, 100mm insulation between 150mm rafters, membrane, battens, OSB, felt. There are small gaps in the battens top and centre at each gable end with insect mesh over each and then its open all along the bottom edges by the fascia/soffit but covered with insect mesh again.

The other difference is the base of the wooden frames are sat on single skin brick, 2 courses on the edge of the slab which itself has a damp proof membrane under to stop rising damp. This is as opposed to the 2 skin with block and 3 courses of brick as per the thread I avidly read and digested. Understand 2 courses, single skin is fine however.

Internally the walls are boarded with 12mm plywood down to the floor.

I'm hoping that you can advise/steer me in the right direction on the following issue I have encountered. Hopefully I've not been a numpty and suffered from ambition beyond my competence!

I should state at this point I am yet to batten out and clad the external walls. The weather has not been great recently and I have struggled for time in the preceding months, with a health issue also preventing progress. The building is wrapped in Powerlon ultraperm membrane with the joints all taped up and is basically weatherproof for the moment.

It rained very heavily here for some weeks. I noticed that there was green mould along the bottom edges of the plywood and also noticed that in one of the corners there was a damp patch on the concrete floor. I removed the plywood and found there to be a lot of green mould all along the bottom edge of the plywood up to the height of the top of the brick course. The wooden frame (sat on dpc) and insulation were all bone dry so its not water coming down from the roof I don't believe. I think this is rain pelting the side of the workshop, running down the membrane, the bricks getting wet and I also noted on inspection that the water seemed to be making its way down between the concrete base and damp proof membrane.

The mould was in fact all the way around the workshop on every wall at the level of the bricks. I have removed all the internal plywood wall (just love undoing work already completed!), treated the mould with some spray I bought and I have now liberally coated both sides and edges with a preservative that will hopefully suppress the mould re-growing. I intend to also apply a matt varnish to the bottom sides facing the bricks, edges and the entire side facing internally. I have not re-attached the plywood yet. This alonq with a long delay on the upvc windows (coloured frames delays due to Covid) with delivery date now confirmed for middle of December (ordered August), I feel like I'm in limbo a bit at the moment and really want to get it completed.

Anyway, none of the above is addressing the cause of the problem. What I am looking for is advise on whether I need to;

a) just pull my finger out and get on with cladding the exterior as quickly as I can and that will largely resolve the issue. My only reservation in assuming this will sort it is something that happened a couple of weeks ago mentioned further down.
b) look to apply some weatherproofing sealant to the bricks (Ibstock West Hoathly Medium Multi)
c) Trim the internal plywood so that it doesn't cover the bricks inside (I'm fine with doing this, I have no hang-ups over aesthetics and see no practical issues) as some level of damp could always be an issue with a single skin setup maybe? This doesn't solve the problem of damp bricks/concrete around the edges of the workshop though.
d) do something to seal the damp proof membrane to the concrete. I will admit that I have rightly or wrongly already applied a bitumen rubbery liquid membrane in an attempt to do this prior to the heavy rains as I need to build up the ground on two of the sides and the membrane was such that it would make a great rain collector. That was fine but it hasn't bonded the DPM to the concrete very well in some places thus probably rendering it completely ineffective! There is a 50mm portion of the concrete base above ground level, DPM stops about 50mm short of this so is at ground level apart from on two sides as mentioned. I have been careful to ensure that I haven't got the liquid DPM on the 50mm odd of exposed bit of concrete. In terms of the seal between the DPM and concrete its good about 80% the way round I'd say, with some gaps that I could address. Corners with folds are the main challenge.
e) Combination of the above?

Someone did suggest cladding all the way down over the bricks externally but I don't want to do that as it defeats the purpose of the brick course and will inevitably mean the bottom edge of the cladding rotting away relatively quickly.

The other point to note is during a particularly heavy downpour two weekends ago, with rain pelting one corner in particular, water was soaking out of the brick internally onto the concrete inside, literally forming a puddle as I stood there watching it with a depressed look on my face!

I am open to all suggestions at this point and don't believe in any way its an issue in the design I have followed but more than likely an issue in the execution of said design as applied to my build or also a consequence of not having finished the outside just yet.

I wanted to get advise now before continuing further so that I don't end up having to undo or redo anything. Happy to share pictures if needed if it will help, I've taken quite a lot throughout.

Thanks
Toby

 

[TrimTheKing]

Hi Toby and welcome

Can I suggest you stick a load of photos into the thread to demonstrate each of the points your raise. I'm finding it quite hard to visualise a few things so putting pics in there would probably help significantly.

 

[greeno]

Sounds like, a you said, the rain is running down the membrane and saturating the bricks. Cladding with a drip edge should pull most of the water away.

As belt and braces you could put a couple of coats of black jack or similar on the inside.

 

[greeno]

Have you got a roof and gutters on a well? If not, this would i increase the amount of water running down your wall membrane.

Also, your overlaps, they are the correct way round, aren't they?

 

[Mike G]

Welcome Toby.

The first thing I would do is to make sure that the ground level was down 50mm or more from the top of slab, all round. You worry me when you say you need to build the ground up on two sides........well.......you just can't. Not against the building, anyway. You'll have to form some type of retaining wall away from the building. Then get your gutters done and finished if they aren't already. If you haven't got your cladding on then it is inevitable that water will track along the junction between timber and brick, leaving you with saturated bricks. I built a store shed a year or two back and had precisely this happen in the 6 months or so I left it un-clad, and the matter resolved itself as soon as I put the boards on.

If the building is subject to condensation it will inevitably be at plinth level if there is just 4 inch brickwork. That will be the coldest part of the structure and thus subject to condensation. A combination of ingress and condensation is likely at work here. Removing the ply will certainly help, in that this will allow air circulation which will aid drying the bricks.

I'm afraid that nothing is going to fix your problem until the building is complete, and in particular, until it is clad. Don't, whatever you do, apply a waterproofing to bricks. It's a long explanation, but you will effectively just mask your problem and in the end destroy the bricks. Don't clad over the bricks, either. The cladding forming a drip to take water from the walls away from the top of the bricks is a critical element of the design, and I'd be confident that you will see a transformation when you have completed that detail.

I think we are going to need to see photos before I comment on the Synthapruf-type stuff you've applied, but I just can't see any way that it would have helped you. Cut your DPM off at the point where it turns under the slab. It shouldn't turn up the edges. As you have noted, this will just hold water.

I believe there is a low threshold of posts (something like 3 or 5) before newcomers can post photos, so just respond a couple of times here then fire us some piccies. Things are much easier to discuss when one can see the actual issues.

 

[tohowe]

Thanks for the replies all!

TrimThe King, thanks for your response, having reviewed the photos I do have none of them really focus on the slab detail so will take some and post up tomorrow morning.

Greeno, thanks for taking the time to respond. Yes agreed, I have got guttering on now as of this weekend just gone so hopefully that will help as you say and yes my overlaps are the right way round, with top most overlapping bottom with this being the case with the roofing membrane, felt on the roof and also the membrane around the building etc

Mike, thanks for taking the time to respond. Yes as the saying goes a picture paints a thousand words. I'll get out first thing tomorrow and takes some specific pictures I think as what I have already aren't particularly helpful to this issue as they are of the main building/build as opposed to the slab/DPM etc.

Not sure if adding this photo will work but here goes anyway. It's a not particularly good photo that shows the end nearest the house but its not all that helpful in seeing the detail at the slab level!


Just on the point about building up the level on a couple of sides, what I meant was that the ground is/was not entirely level all around the slab so I chose the corner (nearest the house) when levelling the shuttering to be where the top of the slab would end up (about 50mm higher than the ground level at that location) This was the highest point overall and so the level flowed out to the other corners. The opposite end of the slab, the ground was much lower such that when I removed the shuttering, after the concrete was poured, the bottom of the slab was as near as damnit level with the ground. I was referring to raising this ground level earlier.

I think I have quite possibly misunderstood the way the DPM is supposed to work in this respect as I have it turned up the sides which is clearly acting like a big bucket at the moment with the slab in the middle! I had always thought it was turned up the sides and surrounded the slab, held against it by the soil or whatever. One challenge I might have here then is that the area at the far corner can get quite waterlogged, possibly why I had it in mind that the DPM turned up the sides etc.

Thanks
Toby

 

[tohowe]

On seeing the last picture I added on the post I decided that with the wonders of modern technology (a torch) I'd snaps some pics just now.

As you can see I have added drainage which I forgot to mention previously. This is all the way around. Hopefully you can make out the membrane along with the bitumen stuff I applied to attempt to seal the top edge of the DPM to the side of the slab








Hopefully these show enough detail. I guess I'm hoping I haven't created the very issue I was in fact thinking I was avoiding/mitigating my slathering on this gunk in the fist place! With some time, persistence and diligence I could probably get rid of a lot of it if needed. I suspect nature, weathering and time would probably do it as well...

 

[tohowe]

Also forgot to add that the slab is C30 and is 6 inches thick around a 10 inch periphery going to 4 inches thick in the middle

 

[Mike G]

Thanks for that Toby. It's hard to be certain in this light, but it looks like the bricks and slab are dry. I doubt the problem is there. Cut off the DPM as I described and you should be OK with that detail.

It looks to me like your DPC forms a shelf, and thus a route in for water from above. I might be wrong, and a close up photo of that detail would be useful. Again, just doing the cladding will sort this. That is pretty much exactly how water flooded into my store shed in its part-built state.

 

[tohowe]

Thanks Mike. Delayed reply here as I've got tomorrow off so today was doubly busy!

The slab and bricks look relatively dry you are right but the bricks were certainly wet at one point during the various downpours we've had here and a damp meter inside the workshop indicates the corner that I could see water seeping in through the brickwork, still to be quite wet. It will dry out in time of course. I think you are right though in that once I clad it should resolve the issue.

Just about the point on the DPC, the below photo shows the DPC and breathable membrane I have wrapped the building in. I have pulled it back to show the DPC underneath which is folded up and attached in places to the frame. To explain the bottom piece of membrane covering the bricks, I added that the other week as a temporary measure so that if it buckets down again, water dripping down from above would track down to the ground rather than onto the bricks/concrete. Its tucked under the membrane above and will be removed when I clad. I will also trim back the membrane above it inline with the top of the bricks. At present it overlaps onto the top of the bricks by about an inch or so.



Thanks again for your time in responding. I think I am much clearer now on the DPM detail and how this works. Probably should have asked/clarified before I set out on this venture! :eusa-doh:

Best I get on with the cladding!

Thanks
Toby

 

[Hobbo]

Hi Toby, nice looking build.

I had water problems that came from both the roof and from rain splashing up the side. The roof problem was not putting the final roof sheets on soon enough and rain leaking through the roof membrane- especially in places where leaves and twigs had caught up in the lath. I'd also stored a load of wood along the side of the workshop which made an easy point for rain to cause problems soaking the side membrane but then also shielding it from being able to dry out.

I know both of these are a different cause of water ingress to you, but what probably is the same is that once either the timber frame or bricks get soaking wet, they act like a wick. Even after fixing the leak it wasn't until everything had a chance to dry out that water stopped coming in. It really surprised me how easy water came in through the soaked areas especially how porous the bricks became, it puddled inside and I had issues with mould.

I started to doubt that I had fixed the leaks, but once it had a chance to dry I've had no leaks at all. It took quite a while before it fully dried though. Once it dried I added an electric greenhouse heater- it's a tube sort of like a mini oil fired radiator that just ticks over giving a bit of heat and I find that's been enough to keep mould at bay.

I think the advice above is spot on. Just keep faith in what you've done, give the damp a chance to fully dry and you'll be fine!

 

[tohowe]

Hi Hobbo,

Yes I was surprised at how the water was almost running out of the brick inside the workshop during the heavy downpour. I think you are right in that it was already wet from previous rainfall and it therefore didn't take much before it was creating a small pool!

I have made a start on the external cladding now, though not got as far as I wanted due to not having the light during the week and other things taking up time on the weekends. I've noticed that most jobs that I think I'll get done in a day take twice as long, if not longer. I think doing a lot of things for the first time is always like this!

I might consider the greenhouse heater as although I have ensured that the new windows have trickle vents to allow some air movement, a bit of heat probably won't hurt and it sounds like you've had luck with that!

One thing I also intend to do is add a single coat of a matt varnish on the edges, backside from the bottom edge up to the start of the frame and the whole inside face of the internal plywood. That way I hope to limit the plywood holding water. By leaving the majority of the backside uncoated I'm hoping any dampness will evaporate out at the level of the insulation/membrane. We'll see.

Thanks for your words of encouragement and for sharing your experiences, always useful!

 

[Peteh]

Hi Toby,

Looks good. I'm sure you will get the leak sorted.

I had the same problem.

viewtopic.php?f=35&t=4578&start=50#p71144



From the picture, you can see that the breather membrane stopped slightly shy of the brick edge. The brick cavities filled with water and leaked between the brick top and the DPC creating a nice pond in the workshop.

Temporarily I affixed a 150mm strip of DPC under the breather membrane to throw water off the brick. When I came to clad it, I left it in place as a failsafe.

Notwithstanding that, the bricks I used a quite porous so I am not really sure how this will work long-term but I too thought about using a water sealer. Not sure now after Mike's comment.

If I were doing this again, I would do the following:

- All 3 brick courses would be semi-engineering bricks or maybe even full engineering bricks
- They wouldn't have the cavities in the middle (assuming you can get bricks without the middle holes)
- I'd add some SBR or similar waterproofing agent to the mortar mix such that my mortar was also waterproof.

Good luck,

Pete