Leaking Parapet Wall

Case Study

Roofing Contractor: London Flat Roofing Ltd.

Customer : Private

Problem: Leaking Parapet wall and roof

Solution: New Kemper liquid roof over old asphalt roof

Customer told me over the phone that all of the internal damp areas are along the edge of the ceiling with the junction of the external  wall, and that the problem is happening in most of the flats below.

Let’s list the areas where the water could be coming from:

  1. Top of the coping stone
  2. Internal surface of the cracked parapet walls.
  3. External surface of the cracked parapet wall.
  4. The box gutter running along the bottom of the parapet wall.
  5. The flat roof itself and running back to the parapet walls.
  6. Sweating of the roof.

So let’s rule out one or two of the above options:

6. Sweating of the roof.    ( links to a video of a sweating roof)

Probably not, if this was the case there would be more damage further into the flats.
This roof is probably not insulated to the new building regulation standards (Part L1b). Conservation of fuel and power (Existing dwellings).

5. The flat roof itself and running back to the parapet walls.

It’s a possibility, but as you described the internal damage being in lots of areas, I would rule this out.
So now we have options 1 to 4; personally I think you can’t rule out any of them. I haven’t seen the condition of the external parapet wall, so I can’t really comment.
Over the phone you talked about having two quotes and they both differed.

Quotation one

Suggested chopping away all blown render to the internal walls, making good with sand and cement and re-setting the coping stones.
This is a way round the problem, provided the new coping stones with a drip detail is used, or the old copings have a lead drip detail formed under them. Personally I would just change the copings.

Quotation Two

Suggested lining the inside wall with felt and capping the coping stones with felt. I assume that some preparation work will take place before lining the walls.
I prefer this option; it will not look good, but it will be cheaper and I think, if undertaken correctly, should last some years.
The photo to the right is an example of some good felt work dressed up and over a parapet wall and coping stones.

Both quotations don’t take into account the two other areas we pinpointed above.

3. External surface of the cracked parapet wall.

4. The box gutter running along the bottom of the parapet wall.

Kemper is flexible so will take any thermal movement between the change of materials, brick parapet wall and timber decked roof.  Kemper also self terminates, basically sticking to anything that’s primed correctly -take a look at this video:
Kemper can be joined too, so if you want to extend the system onto the old felt roof you can. If you decide to update the roof and the insulation, again you only have to deal with the main roof, yes you will have to insulate inside the box gutter, so you will re-line them but you won’t need to touch the parapet walls, the Kemper v210 system is guaranteed for 15 years and expected to last a lot longer.

Why Kemper over all the other materials?

The above project is very detailed, so a reinforced liquid system is the best; when the liquid resin and the reinforcing materials have been overlapped and dressed into all difficult corners, it sets and you have no joints to leak.
Link to Kemper flat roof over corrugated flat roof and asbestos.

Moving on….

If at a later date you do decide to do the main flat roof, as it’s a big area, EPDM sheet rubber could be used. This is cheaper as it greater longevity, and we could dress this into the box gutter formed from the Kemper i.e. “mix and match”. Preferably I would like to do the complete roof in Kemper, however sometimes on large roofs the Kemper becomes expensive; it’s all down to cost and whether or not it will work.
I hope this helps. If you want me to cost the work for you I would really need to see the property.
Steven Dickinson
078023 00099
By the way you may also be interested in a new venture of mine  www.ecopopulus.co.uk we  do three main things from this side of the business.

As a property owner all three will become relevant over the next few years, part L1b is already impacting upon you.

Speak soon.


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