Waterproof timber frame wall

[Jdwood38]

Good morning,

Can anyone advise on and/or provide sections for the make up of a waterproof timber frame wall? If it's even possible of course!

Short version: need to build a flood resistant wall that currently divides a garage and a room with staircase (originally this room was the second garage). The existing wall is timber frame and currently stripped bare due to said flooding. Plan initially was to rebuild in masonry and then waterproof but that is likely going to require digging out footings and will result in a loss of space for insulation on top of thickness of masonry wall rather than 'within it' with timber frame. We will of course sacrifice and do this if necessary to prevent future flooding but would like to consider all options, including novel, first - after all, you can make a bathroom/wet room/swimming pool waterproof!

Chartered Surveyor who generated the schedule of works for reinstatement understandably requires 15mm Fireline plasterboard on the garage side of the wall so we understand that we need to provide that level of protection.

Things I've thought of so far as possible options (and I'm by no means qualified so these may be nonsense!):

- Board out with Fireline as required, and then skimmed with waterproof concrete based render and painted
- As above but boarding out with cement based board ('Hardie backer' type stuff?) - from memory this may provide the same level of fire rating?
- Boarding out with either of the above and then tiling with waterproof adhesive and grout
- Boarding out with either of the above and then cladding to the potentially highest waterline with either:
- Waterproof concrete based cladding
- Sheets of plastic such as Perspex, with joints and edges silicone sealed
- Sheets of tempered glass (such as that used for splash backs) with joints and edges silicone sealed

Most important thing is that the wall will need to keep out water for a period of submersion of let's say half a day and, if actually required to keep out the water, can just be jet washed down once waters have receded and ideally without having to replace any component. It feels to me like the most vulnerable points will be where any finish meets the floor, existing walls and any joints.

Is this pie in the sky thinking or might there be an option for this? Any thoughts gratefully received!

 

[noseall]

Dig down and build a 3 or 4 course kerb then build off that.

 

[Jdwood38]

Thank you for the response. Unfortunately I'm not sure that would improve our position and I assume would still require proper footings? The water in the garage when we were flooded reached about 0.8m (the property is a 'bowl') so we need to aim to provide a level of protection for up to 1m.

The storm that ultimately lead to the flooding had the biggest amount of rainfall ever recorded locally and an 'annual exceedance probability' of c.0.65% - so there is a 0.65% chance of seeing that level of rainfall again each year. So it is possible that we may never see that level of water again, although the way climate change is going we want to be prepared as best we can. As part of reinstatements we will be fitting flood resistant doors and waterproofing the external walls, there are just a couple of vulnerable points where water entered such as this one which we need to protect. The others are easier as they are rendered timber frame built on top of the perimeter foundations of the property which can be reinstated in masonry without any other changes (e.g. a bay window).

Thanks again

 

[^woody^]

Chartered Duffus if he's specifying plasterboard on a wall that may get wet.

A cement board - Calcium Silicate preferably or Magnesium Oxide maybe, on top of a DPM with sealed joints and abutments for both layers. Simple.

Any timber that may get damp should be preservative treated - preferably pressure treated not just coated.

 

[freddiemercurystwin]

I can't quite picture the scenario where you only need to flood proof one wall to keep floodwater out of a garage, anyway I guess a membrane system employed on the outside would work, assuming the timber frame wall has the structural integrity to resist the water pressure. The likes of RIW or Synthaprufe are commonly used when building concrete flood proof walls, I daresay they would work on timber frame walls too, the devils in the detail though so junctions where your timber frame meets masonry wall swill be weak points unless designed properly, indeed how do they resist flooding? All of your previously considered ideas seem far fetched and prone to failure. You could do worse than speak with Trada.

 

[mrrusty]

How about metal studwork, cement board and closed-cell insulation that won't absorb water - perhaps expanded polystyrene

 

[Jdwood38]

Chartered Duffus if he's specifying plasterboard on a wall that may get wet.

A cement board - Calcium Silicate preferably or Magnesium Oxide maybe, on top of a DPM with sealed joints and abutments for both layers. Simple.

Any timber that may get damp should be preservative treated - preferably pressure treated not just coated.

Thank you Woody. I should be clear in the defence of the Surveyor that the schedule of works was for insurance purposes only and therefore had to be specified to reinstate like-for-like as anything else would be considered 'betterment'.

I will have a look at those boards. Can you advise any sectional drawings that might show the DPM detail, especially around the bottom and sides. I will of course try and Google myself but usually lack the terminology to find the exact thing! Hopefully the timbers would not be getting wet at all, otherwise we've probably failed in the aim!

 

[Jdwood38]

I can't quite picture the scenario where you only need to flood proof one wall to keep floodwater out of a garage, anyway I guess a membrane system employed on the outside would work, assuming the timber frame wall has the structural integrity to resist the water pressure. The likes of RIW or Synthaprufe are commonly used when building concrete flood proof walls, I daresay they would work on timber frame walls too, the devils in the detail though so junctions where your timber frame meets masonry wall swill be weak points unless designed properly, indeed how do they resist flooding? All of your previously considered ideas seem far fetched and prone to failure. You could do worse than speak with Trada.

Apologies that it wasn't quite clear. The garage is, at the moment, be mostly sacrificial so that if it happens again, there is a larger volume of storage to keep any external levels lower. This wall divides an existing double garage that has had the one half converted. So this is to keep water that comes into the garage from coming into the house - hopefully that's clearer!

Thank you for the good advice which I will certainly investigate further. However I'm not familiar with Trada?

 

[Jdwood38]

How about metal studwork, cement board and closed-cell insulation that won't absorb water - perhaps expanded polystyrene

Thank you, I shall add this to the list of possible options!

 

[freddiemercurystwin]

Apologies that it wasn't quite clear. The garage is, at the moment, be mostly sacrificial so that if it happens again, there is a larger volume of storage to keep any external levels lower. This wall divides an existing double garage that has had the one half converted. So this is to keep water that comes into the garage from coming into the house - hopefully that's clearer!

Thank you for the good advice which I will certainly investigate further. However I'm not familiar with Trada?

So how do you know the other walls won't flood assuming you make your new timber frame wall flood resistant?

Trada may (or may not) be helpful: https://www.trada.co.uk/about-us-menu-pages/contact-us/ phone the tech advice line

 

[^woody^]

Thank you Woody. I should be clear in the defence of the Surveyor that the schedule of works was for insurance purposes only and therefore had to be specified to reinstate like-for-like as anything else would be considered 'betterment'.

I will have a look at those boards. Can you advise any sectional drawings that might show the DPM detail, especially around the bottom and sides. I will of course try and Google myself but usually lack the terminology to find the exact thing! Hopefully the timbers would not be getting wet at all, otherwise we've probably failed in the aim!

The DPM is either cut into a 25mm chase in the walls and floor or bent around and under the frame so its between the frame and the walls/floor, and either way then sealed with a bead of polymer/butyl/silicone mastic.

The alternative with a seal around the DPM with butyl tape leaves the tape visible and is a bit crap.

When the cement board is fitted, you seal the back edge with the same mastic as above, but the front edge needs to be intumescent mastic.

 

[Jdwood38]

Thank you all for the assistance in trying to solve this one. As always a good selection of responses and advices. We've opted to go down the masonry route to ensure that it can be properly waterproofed.