Barn to annex conversion

[LBCarpentry]

About to embark on a conversion of an old wood store barn into a small annex. See images attached. I intend to repoint the interior stonework with lime mortar but then I need to (I presume) fully waterproof 3 of the 4 walls to stop damp coming through. The barn is open at the front, but because we are on a hillside the rear and two sides are buried - again see photos.

What would you do to waterproof it to stop damp coming through? Is there a damproof / waterproof coating I can paint the internal walls? My intention was to paint the brickwork and have surface mounted pipes for services and not sure how I would hide electrics yet. Obviously if there is a waterproof membrane on the walls, this means I can't fix anything to the walls after. Need some advice on whats best

Don't particularly want to line or stud the walls as I want to maximise space and retain a rustic feel. But I certainly don't have many options on my side.

Thoughts on a postcard!

 

[eribaMotters]

I cannot really see painting anything on the inside is going to be successful. You either need to dig around the wall outside to stop the water getting in or do a tanking job on the inside which would be expensive. What ever you do at the end of the day you need to get the damp levels down as it will play havoc with both timber and tools.
As regards services, I'd drop them from the ceiling. They do not have to be attached to the walls.

Colin

 

[LBCarpentry]

Unfortunately digging around the outside is an absolute no go. I did think tanking would be an option

Thanks for the input

 

[Adam W.]

You can tank it sucessfully............As you have a semi-basement you'll be best off using this product.

https://gcpat.uk/en-gb/solutions/products/hydroduct-drainage-composite/hydroduct-cf
Be warned, that it's a lot of work to install and requires careful attention to detail and thinking™ for it to be watertight.

 

[LBCarpentry]

hhhmmm yes i'm never entirely sure what tanking is but that is pretty much what I imagined. I don't want to have to build an internal though as space is tight. But if thats the only option then that will be the answer. And you right, looks like a hell of s lot of extra work on top of what is already going to be a reasonably big job

 

[LBCarpentry]

I would be nervous about a product like that also. It's a stone wall that was never designed to be flat or smooth (as its a barn obviously) so the variation is really quite big in places. I actually think it would be easier, and certainly cheaper to dig out the entire edge and try to line the exterior walls with a DPM of some form. The ground at the rear of the barn sits 1.8m high up the wall. This is the highest point.

 

[LBCarpentry]

Drawings coming on nicely though
Figured I would have to create a new bathroom as there simply isn't space in the current structure. So up the project goes. Time & Cost

 

[Adam W.]

hhhmmm yes i'm never entirely sure what tanking is but that is pretty much what I imagined. I don't want to have to build an internal though as space is tight. But if thats the only option then that will be the answer. And you right, looks like a hell of s lot of extra work on top of what is already going to be a reasonably big job

Yes, I did a couple a while ago, but it works really well. The advantage of an internal block wall is that you can fix stuff on the wall, whereas all the other resin paint on tanking systems that I looked at would have been compromised by drilling.

 

[Blackswanwood]

There are three types of tanking - cement based, bitumen based or a plastic barrier product such as the one suggested above. They all need attention to be given to drainage as when the water cannot come through the wall it has to go somewhere else.

My guess is that taking the existing structure out and starting from scratch is likely to be easier and more cost effective.

Sorry to sound cup half empty and good luck with finding a way to get the bathroom of your dreams!

 

[Adam W.]

The one I mentioned needs to have the barrier go all the way across the floor and gets drained down the edges to the outside in a gravel gulley. Gravel is poured down the back of the membrane to keep it away from the wall once the insulation and blockwork is in place.

It's quite thick and very tough. I also use it on green roofs to protect the membrane and create a water store in the dimples.

It's and industrial grade tanking system that they use on large commercial basements.

 

[Fitzroy]

Personally I’d be very nervous about messing with the surrounding ground. It’s a significant slope behind the building, I’d be worried about the wall integrity without the earth and/or the integrity of the remaining hill if no longer butting against the wall. Perhaps the ground behind the right wall would be ok, but the rear wall, I’d be seeking professional advice if I wanted to touch that.

 

[TomGW]

Personally I’d be very nervous about messing with the surrounding ground. It’s a significant slope behind the building, I’d be worried about the wall integrity without the earth and/or the integrity of the remaining hill if no longer butting against the wall. Perhaps the ground behind the right wall would be ok, but the rear wall, I’d be seeking professional advice if I wanted to touch that.

If using the above tanking system on the outside it should be backfilled with gravel, with a drainage pipe at the bottom. However, it’s designed to also be used inside on walls and floor, all sealed together, with a drain to take the water out out the building. Fitted properly, it works excellently.

 

[AJB Temple]

The building is small but will still cost an arm and a leg to tank, insulate and put a proper roof on. It makes no sense at all and would be far better, cheaper and quicker to prepare another spot for a purpose built structure fit for purpose.

 

[RichardG]

I would think about removing the roof and all the wood work, repointing the wall and making good and then consider the old building structure as a retaining wall. Use the existing base (if good) and then create a new building with all the insulation etc. I'd make sure the new roof overhung the old wall to keep the worst of the weather out and place drainage to keep the gap between the new building and wall dry.

If you want to make the wall look part of the new building then space cladding off the rear and side walls so the bottom of the cladding sits just just on the wall.

I have seen a few bad experiences with tanking, it's expensive, has to be fitted to a very very high standard, and yet still fails due to ground/building movement or later trades sticking a drill through it and not telling anyone or not realising it was an issue.

 

[TomGW]

The building is small but will still cost an arm and a leg to tank, insulate and put a proper roof on. It makes no sense at all and would be far better, cheaper and quicker to prepare another spot for a purpose built structure fit for purpose.

I have to agree. Apart from the technical difficulties of the tanking operation your main issue is that the building isn’t big enough for the intended use and will have to be extended anyhow.
If this it the optimal location for your annex, why not demolish, excavate and build a new build with proper tanking, then use the stone to clad the outside above ground? Much more involved and expensive than you were originally considering but likely the best solution in the long run.

 

[Lons]

I agree and as an ex builder with some experience of grade 2 and stone buildings I'd demolish all but the rear retaining wall of the building and start again, you'll never successfully convert the existing given you've clearly stated you can't lose any interior space and the work will be expensive in any event.
Easier, quicker, possibly cheaper and far better to get the dry and insulated space you need by starting from scratch. Re use the stone if you want to keep the old look and buy in some matching stone, it can be as cheap as bricks if you look around.

 

[Jones]

I'd use a tanking membrane as it can cope with a bit of movement whereas a cement slurry would crack then be less effective. The fixings are usually hammered in ,you can then screw battens to the fixings and board that , but in a stone wall it's unlikely you could do a good job lining it all up and getting good fixings that are moisture proof. If you just hang the membrane from the top and build a false wall Infront you can avoid fixings in the damp part altogether and you have a straight wall on the inside . You need a drainage channel round the perimeter below finished floor level. Also a good roof overhang with gutter at the back will keep water away from the back wall.

 

[LBCarpentry]

Well it’s sounds almost overwhelmingly like it’s a bad idea to work with this structure. Which is a real shame. But that’s why I asked here.
Back to the drawing board then and design a new building to go in its place so you’d better wait for more questions.

This also opens the door for me to have a go with SIP boards which I’ve been wanting to play with for some time. I will design an annex of similar size and then I can make it fit into the surrounding area.
Better buy a new spade and pick axe I reckon.

If anything it will be a good practise run before I take on a much larger conversion which will be happening to my house which is next to this building.

 

[Adam W.]

By the loks of it, you'd be better off with a mini digger and dumper.

 

[Daniel2]

By the loks of it, you'd be better off with a mini digger and dumper.

I also agree.
Far better, and probably ultimately cheaper, to remove the existing
structure. Then prepare a fresh starting point with a mini digger.
There really isn't much to be saved with that existing building.