How to build studio wall against retaining wall?

[Trobo]

Hi,

We are currently undertaking large backyard renovations and I will be performing a large part of a studio build as part of that.

The concrete slab is already laid and 2 sides will be easy to frame and clad on as they are open and the edge of the slab falls off into garden and landscape areas however 2 sides will be up against besser block retaining walls, one will not be very high but the other will be about 2 thirds of the way up the studio wall in height from the slab. The plan is to have a small cavity (100mm) between the retaining walls and studio so there is no risk of water finding its way through the walls by direct contact but there will be a small cavity with no room to really perform any work in that cavity so I had a few questions as to how I should build those walls.

I plan on it being a timber frame and likely weatherboard cladding studio with an external wrap between the frame and cladding and my questions relate to how to get the wall built while getting it weather tight.

The retaining wall sides are completely hard surfaces with the concrete slab butting up to concrete besser blocks there is no drainage on them (agg lines and drainage behind the retaining walls and once the studio is up the gutters will overhang the cavity but still a small chance of water finding its way down there). So I want to make sure I have a complete seal around the bottom timber plate so water cant soak through there at any point.

1. Should I therefore put in a bottom plate around the entire external wall into the slab first (its simply a rectangular build) secure it to the slab with a damp proof course between them and then I was thinking to silicone the join at the bottom of the frame too in case of any sitting water in that cavity?

2. If I do the above should I use treated timber for that bottom plate just as an added protective measure or no point?

3. I was then thinking (for the studio walls against the retaining waters) frame them up on the ground as I would do with the other walls but then also brace, wrap and clad them possibly just simple sheeting as it will be hidden (at least as high as the retaining wall where I wont be able to work behind) while on the ground so I can then stand them up on to the bottom plates I have already attached and can then connect them through into the slab effectively ending up with a double bottom plate. Is this the best approach as I cant think of any other way to make sure that I can get those walls built?

4. Is there anything I can or should add into the cavity between the walls to try and drain out any water that may find its way in there so I don't end up with any standing water?

Any other considerations I should account for as well would be a good help thanks.

[Dave-1]

Afternoon @Trobo 

I am excited to see the project when you are finished! Envious as that sounds like a nice space to build.

Welcome to the Bunnings Community If you take a wander through a few searches I am sure you will get a lot of ideas for your build.

I like the way you have approched the water issues and how to work around them. The air gap between the retaining wall and the rear wall of the studio is 100mm and that makes me pause a little. With an eave overhanging it, there wont be a lot of air movement to keep the area dry?  And the only other thing that omes to mind is the retaining wall top sitting above the grond or level? Just thinking of water running over the top from the ground is all.

Looking back at your description I wonder a line of brickwork for the timber to sit on so there is no chance of the timbers sitting in water?

Last question Is there a chance for a photo of the area? Seriously would love to see the project unfold as you work through it.

Dave

[Trobo]

Hi @Dave-1 I don't have a recent picture of the area but will take one once all this rainy weather has passed to give a better view of the area as the short section of retaining wall will only be a few blocks high (less than 1 metre) and then has an elevated deck in that area behind it up to a pool surround. The longer wall is the taller one roughly 1.8m tall and will have lawn there with a garden bed running along it, it will have stone capping on it so it will be slightly above ground level so chance of water running over is not a concern, moreso just rain coming in at an angle getting into the cavity. As for the wind due to the ends of the larger retaining walls being mostly open and not enclosed at 90 degrees hopefully it will still allow enough airflow as we do tend to get a nice breeze through with the backyard being a bit elevated but yeah not entirely sure.

I hadn't considered a brick course as an option but I also have no experience with bricklaying and more comfortable with timber so not sure I'd have the cleanest brickwork if I was to go down that route. I also wonder about the issue of having brick around the edge where I'll ultimately have flooring specifically skirting inside having to connect to the wall and the hassle of that being into brick vs timber.

[Dave-1]

Afternoon @Trobo 

It makes sense what you are saying about the water and the capping stone on the retaining wall. Maybe make the roof eave wider and that way stop rain at an angle? You do seem to have it sorted tho

I havnt done brickwork either, I was thinking of something that wont rot or perish. As to the flooring and associated skirting. The skirt could still cover the bricked layer with the timber frame on top if you went that way. The skirt and the flooring arnt actually attached, the skirt kinda sits on the edge of the floor. I use to be so concerned about it until I changed my skirting over and then it was "Really?" its that simple? lol Kicked myself afterwards for stressing. 

Dave

[EricL]

Hello @Trobo 

Allow me to welcome you as well to the Bunnings Workshop community. It's marvellous to have you join us and thanks for sharing your question about building a studio.

It's great that you've received excellent advice from @Dave-1. My main concern is that you won't have access to that corner of your house should any rain damage occur. Would it be possible to move or shift the entire structure 500mm away from the retaining wall. This will give you enough space to slide in sideways and secure the weatherboard corner of your studio.

That access space will also let you bring in tools and provide adequate airflow preventing condensation from forming on the surface of the retaining wall and the studio.  

However, if moving the structure is not possible, I can only suggest making sure that the walls are weather tight.

Let me call on our experienced members @TedBear and @homeinmelbourne for their recommendations.

If you have any other questions we can help with, please let us know.     

Eric

[Trobo]

Hi @EricL unfortunately we cant move the structure as we have excavated a lot of material to allow the slab to be in the position we have so cant move it and shrinking it would mean we lose a good 15% of the floor space so dont want to do that as its not an overly big studio anyway.

And yeah Ive been looking to wrapping and then clad it to achieve the weather tightness. Im wondering if there is any other approach to what I mentioned in basically framing, wrapping and cladding on the ground before standing so I can do that or would that be the best option?

[MitchellMc]

Hi @Trobo,

Building that close to a retaining wall is typically not considered and I recommend you enlist the services of a builder to discuss your options. I would suggest, at a minimum, that the slab should be cut back 100mm from the retaining wall and a drainage channel be installed. That way, any water that finds its way through the retaining wall's face, over it, or from rain at an angle will be taken away. Placing a timber structure that close to a retaining wall isn't something I'd expect you to find a builder willing to do, they'd probably recommend you go all brick.

I like @Dave-1's idea of adding a course of bricks around the rear two walls and building on those. That way, you can install the drainage channels, add bricks, and waterproof them. A dampcourse layer will then be installed, and your timber studs will be on top of it. 

Your idea of constructing and cladding the walls first could work, but I think you'll find that once you have, they'll weigh several hundred kilos and be a bit difficult to relocate. You'll also need to consider how you'll add trimwork in the back corner to cover gaps.

Please let me know if you have any questions.

Mitchell

[Dave-1]

Eveing @Trobo 

Was just thinking about your project and reading @MitchellMc's and @EricL answer. Valid points they make. 

I was thinking of another way, more effort but maybe it could work.

For those two walls that are backing onto soil how about build up a bessa block wall with reo inside it so its a solid wall, waterproof/seal  the layers as you go up and put in drainage at the bottom. That way you get to keep the space, you get to backfill the wall and could even convert the wall to a timber frame once its above the ground?

Dave

[Trobo]

Hi @Dave-1 @MitchellMc the retaining walls in place have been built in besser blocks, core filled with concrete and are rebarred into the foundation and slab so the walls and slab are all combined into a solid structure so there is no risk of movement as its holding back a fair bit of soil and a pool that is elevated above the structure and they have been waterproofed on the opposite side to where the studio will sit (the soil side) with agg lines (slotted PVC pipes), geotech fabric with agg fill so draining on that side should find its way into those pipes and drain out.

I'll look into the brick course option to raise the frame up, is there any other way of erecting a structure close to an existing wall without first cladding it all lying down. I may just need to get a few guys to help me lift it up if thats the only option as I couldnt think of any other way of doing it.

[Dave-1]

Afternoon @Trobo 

Could you use the bessa block retaining wall as a wall then?

As to another way of framing up, you could do it in segmants, either half the width or a third the width and then stand that section up and screw them together, (stud to stud) Think the middle section with a vertical slat that is half on the 1/3rd section and half overhanging so when the two outer segmants are done they can be screwed through to it and seal the wall. The pink bits are the 'spanners" that will be behind the wall to join the segmants together, The black dots are screwing the timbers together

Dave