Newly Created External Terrace Causing Damp


Postby dampproblem » Sat Jan 25, 2014 7:17 pm

Hello

I bought a detached Victorian house from the 1880s. The previous owner has created on all but one side of the house terraces. They look nice, but mean that now soil is touching the outer wall above floor level. As a result of this there is now damp on some of the interior walls (but only where there are the newly created terraces), in particular where plants have been put up close to the outer wall. The surveyor is not sure whether a physical damp proof course exists. The house has a suspended timber floor. There is no basement in most of the affected areas.

The surveyor's main suggestion was to build an aco drainage around the house. Does that make sense in your opinion?

If yes, how exactly would you construct the aco drainage? 1) How close to the exterior walls of the building should it be? I was thinking that as the terraces have been newly created, there should be no structural issues exposing the outer walls and putting the aco drainage right next to it, as this would have the advantage that soil is no longer touching the wall 2) Would you put an insulation layer on the newly exposed parts of the outer brickwork? The current owner is currently applying waterproof paint, but both the surveyor and a builder I spoke to said that this would only last for a few years. The surveyor recommended asphalt or a heavy felt, but the current owner raised the issue that this would not let the wall breath. Which sort of water proofing would you recommend? 3) How exactly would you recommend to construct the aco drainage? I saw on the web, that there are pre-fabricated aco units, i.e. the actual channel/tube where the water flows plus the grid on top of it. The surveyor, however, recommended to dig a channel and clad it with concrete and then put a grid (aco) on top of it. 4) Or would it be the best solution to remove soil as deep as it is required so that the ground level next to the wall is 20cm below the inside floor level and rather than putting the aco drainage inside this channel, to dig even deeper and put the aco drainage such that the upper end of the aco drainage is 20cm below the inside floor level? 5) Would you recommend, additionally, to inject a chemical damp proof course? If yes, where should it be, just below the inside floor level? 6) Would you recommend replastering the internal wall and if so which type of plaster would you recommend, a moisture repelling one? 7) Once there is drainage via the aco - is specific rainwater splashback protection still required, like for instance a transparent silicone paint, or does this again raise issues of how the wall can breathe?

Many thanks for your help.
dampproblem
Posts: 3
Joined: Sat Jan 25, 2014 6:44 pm

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Postby welsh brickie » Sun Jan 26, 2014 6:42 am

With a suspended wooden floor there has to be airbricks to allow ventilation under the floor to dry out any moisture, if these are blocked your floor will rot.
you need to clear the area from around your external wall, so its below the air bricks, aco drains can be installed tight to wall perimiter below the airbricks, then a concrete edgeing must be fitted against the drain to prevent soil fouling the drain system
any waterproof barrier paint wont work long term, the area must be clear to allow airflow.
hope that answers your questions
welsh brickie
Posts: 1972
Joined: Sat Apr 12, 2008 7:54 am


Postby dampproblem » Sun Jan 26, 2014 10:29 am

Many thanks Welsh Brickie, this is much appreciated; the air bricks actually appear to be alright, when the terraces were constructed, ventilation tubes were brought forward, all the way (about 4-5meters) to the edge of the terrace, keeping the airbricks with access to the outside.

The proposed solution will result in quite a deep trench around the house, about 60cm deep, in order to expose airbricks and be something like 15cm below where I think the DPC should be; plus in the beginning I need to dig even deeper, in order to fit the Aco drain at the bottom of the trench. Do you think I could put a grate on top of the trench, at terrace ground level, or is this just asking for trouble, as then water will be splashed back and can flow against the outer wall above the DPC?

I was thinking to fill the whole trench up with pebbles, in effect creating a French drain, but the risk I see here - apart from the notoriously high maintenance - is that the pebbles will not direct all the water strictly vertically down, but some will continue to flow against the wall above DPC level.

How many cm would you leave between the lower edge of the airbricks and the bottom of the trench, so that there is no risk of water spilling from the Aco drain through the airbricks? Or can I stick with the current solution, and leave the airbricks connected to the outside via the ventilation tubes?

Did I understand you correct that the entire trench wall, i.e. obviously not the exposed outer house wall, but the one facing the terrace, has to be clad in concrete, in order to prevent collapse and fouling of the drain? This will be quite an expensive job, correct, given the total Trench will be so,etching like 35 to 45 meters long.

Many thanks again for your help!
dampproblem
Posts: 3
Joined: Sat Jan 25, 2014 6:44 pm


Postby welsh brickie » Sun Jan 26, 2014 6:01 pm

ok now I understand, with the airbricks piped then it should be ok, forget the aco drain dig away the soil and apply a waterproof self adhesive membrane to the wall you may need to paint the wall first with buitumin
then to protect the membrane polystyrene sheets are placed against it then backfill it with soil
welsh brickie
Posts: 1972
Joined: Sat Apr 12, 2008 7:54 am


Postby dampproblem » Sun Jan 26, 2014 6:13 pm

Many thanks for this Welsh Brickie, this was very helpful!
dampproblem
Posts: 3
Joined: Sat Jan 25, 2014 6:44 pm


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