Parapet Wall leaking damp below

[OllyinGoring]

Hi,

This is my first time here and being a homeowner and not a builder/roofer go easy on me!

We have an adjoining parapet wall on a groundfloor extension which is leaking damp through the wall just below the ceiling, with signs of previous damp all along the wall.
Pic 1 &2.

From the outside it seems the mortar is failing?..
Pic 3.

I’ve peeled back the lead work to see what state it is behind, although not sure what it should look like although many of the bricks are damp. Are the light streaks on the lead from the mortar breaking down form water?
pic 4.

Pic 5.

pic 6.

pic 7.

pic 8.

No water pools in this gulley so I think it must be to do with the mortar under the Coping stones? Please advise on what you think the best next step is. I’m up for trying things myself if they are relatively simple, as it’s a groudfloor extension I can easily access without ladders.

Also, as it’s a shared wall with next door am I right thinking costs are shared evenly?

Any help is most appreciated,
Olly

 

[sxturbo]

I've actually had this in the past on my previous house, however my house never had the coping stones as part of its design.

the problem you have there is the mortar. i think someone has installed the lead flashing at a later date to try and remedy the problem. Parapet walls are imo a terrible idea and should only be used on garden walls. they cause so many issues. they are ok if designed properly but the problem is very few people know how to design them.

I had water running the behind the flashing under the felt and caused damp and mold in the rear wall. i sorted it by having the felt removed and a fibre glass roof installed that also capped the parapet so it was a coping stone aswell. i asked them to mount the edge 50mm away from the outside of the wall so there was no chance of water running down the wall. Then as added dose of security i got a clear type water repellant paint (https://www.bcprofiles.co.uk/sika-water-repel-5-litre/?adTribesID=ed1c99a67252918a1e99065fc33086ea|adtribes|9401&utm_source=Google Shopping&utm_campaign=BC Profiles&utm_medium=cpc&utm_term=9401&gclid=EAIaIQobChMIi4WOqLK46AIVzLTtCh1pFA92EAQYAiABEgIvfvD_BwE )
to keep the wall from sucking in moisture. i never had an issue then.

you have a step in the parapet, imo this will create an issue as water will enter via that step. its like having a stepped damp course its not going to work.

Best thing to do is to remove the coping stones, and go up and over the wall (capping) with the fibreglass and have it taper off into the drain gulley, all you problems will be definately solved with this. however it might not look as nice as coping stones.

 

[bobasd]

is that parapet on a shared party wall?

The best course of action would be to demolish the parapet to just below roof level on the lowest side?
On either side of the parapet any lead gutters might have to be lifted likewise the last course or two of tiles.
Then the whole thing re-built on sound principles.

 

[noseall]

Parapet walls - horrendous idea and to put one in the location shown above is madness. The whole thing needs capping in lead.

 

[catlad]

I would try making it all one level.

 

[OllyinGoring]

Thanks a lot for your replies.

So it’s a dividing wall between us and the neighbours. The level is the same either side I think. In pic 5,6,7 It looks like there is a sheet of something between the bricks, what is this?

If I take the coping stones off and chip off the mortar and replace the mortar & stones, will this not stop water from seeping through the gaps? How long might this be effective for?

Demolishing the wall seems quite extreme-surely there’s a way to make it more impenetrable?

Thanks again for all your help

 

[sxturbo]

Thanks a lot for your replies.

So it’s a dividing wall between us and the neighbours. The level is the same either side I think. In pic 5,6,7 It looks like there is a sheet of something between the bricks, what is this?

If I take the coping stones off and chip off the mortar and replace the mortar & stones, will this not stop water from seeping through the gaps? How long might this be effective for?

Demolishing the wall seems quite extreme-surely there’s a way to make it more impenetrable?

Thanks again for all your help

Re-read what has been written.

Repointing and seating the caps is not going to solve your problem. The problem has been attempted to be "fixed" previously by the looks of it, and obviously unsuccessfully.

There has been 2x other possibilities that do not require you to remove the wall in its entirety.

Remove the capping stones, then either completely cap the wall with lead, or cap it with roofing fibreglass.

A 3rd possibility is to cap with a rubber roofing membrane.

However all these options will require the wall to be repaired properly first.

You won't be able to cap with tar based roofing felt.

This will solve your problems.

The netting appears to be some form of damp course but I don't know 100%.

 

[bobasd]

Why would i advise you to demolish & rebuild if i thought that there was an easier, softer, cheaper way of doing the job properly?

The original parapet build was wrong, and later remedial measures appear to have worsened the original problems.
The parapet is unstable and no amount of pointing or capping will alter that. In fact, capping might hide the instability and create a potential risk of wind collapsing masonry?
Plus, as i indicated above, the flashing gutters might be implicated in any leaking?

Your pic 3 obviously shows the roofs on either side of the parapet at different levels.

Discuss this matter soonest with your neighbour's.

The "sheet of something" is a fabric DPC that doesn't appear to have been too successful.

When you open up inside the roof (pics 1 & 2) you will probably find far more water damage than now appears.