Fitting a cavity tray lots of questions?

[mbuckhurst]

I've just discovered 2 major problems with my house, it's about 40 yrs old and is built in the way of the prevailing wind and rain. They've built an extension about 20 years ago, which seems to have a few issues:

1) With the ceiling stripped, after very heavy rain, a damp patch appears on the ceiling, in the middle of the partitition, where a first floor extension has been built onto the side of the house, I'm guessing this has no cavity tray as there's no weep vents in evidence.

2) There's a chimney stack, where they've taken the chimney away from downstairs, but left the stack resting on the plywood forming the basis for the extensions flat roof. When it rains after a couple of hours of continous rain we see a lot of damp patches appearing in the room below.

3) On windows on the prevailing weather side, we've got retro-fitted concrete lintels, after ripping of the tiles on that wall it's become clear the dpc which acts as a barrier to the water above the windows is no longer bridging the cavity and therefore rather than directing the water to flow around the window, it now comes straight through on the inside of the window.

I'm proposing to use cavity trays like these http://www.dpcproductsdirect.com/product-detail.php?pid=23 straight ones for the extension wall and lintel, left and right corners for chimney stack.

I'm guessing these problems require cavity trays, but there are a few potential issues I'd like advice on, in all cases it's only when there's very heavy rain do we notice the damp, but I'd like to stop it for once and all:

1) The house has cavity wall insulation, would this make it hard to insert after market cavity trays, such as those from DPC Products Direct, or is it simply a case of removing enough insulation to get the tray in?

2) The chimney stack is an external left and right angle, but is narrower than the 2 proposed cavity trays, should I cut them down and perhaps use sealant? Removing the chimney is not really an option at this moment.

3) Above the concrete lintels, is it sensible to fit a cavity tray? or is there some other technique that's used by the trade to ensure water on the inside flows back out. I've see lintel end stops and weep vents, but presumably a concrete lintel is flat and level, so there's nothing forcing the rain water to the outside, and a weep vent wouldn't help?

4) If I do fit cavity trays, are these best done at the same level as the flat roof membrane enters the wall, or should it be fitted a brick course higher?

5) Is it normal to to put mortar under the tray or should the tray rest directly on the brick below (or roof membrane in the case of 4) above), presumably the brick that sits in the tray is then mortared into place with mortar on the tray and under the brick?

I hope I've made these questions clear enough? Are my proposed solutions going to work or is there a better way?

thanks for any help

mike

 

[^woody^]

Basically, yes fit fit a cavity tray to lintels that have none

You can buy those ones, or just use some wide DPC and silicone, and leave weep holes.

The tray can exit at the level of the flat roof flashing but better if its the course above.

The tray should be bedded to form a bond, but check that particular manufacturers guidelines.

Cavity trays are for cavity walls and your proposal for the chimney is a bit concerning. You don't really want to be chopping around the chimney too much as you could destabilise it, and also form a weak joint with the potential for the stack above to slide on the DPC.

Whilst a chimney would normally have a DPC when built, you should be sure that you know what you are doing and how to go about fitting one retrospectively. Be sure the chimney problem has the same cause as the wall problem before messing with it.

Also check the pointing to see if its letting too much moisture through

 

[mbuckhurst]

Thanks for the reply, I think trays will suit the problem best - when we get a week of solid rain, the water coming through can be quite significant.

I know the chimney has the same problem because when I had the roof repaired (unfortunately I wasn't around when the guy did it), apparently several courses of bricks fell down when he removed the old chipboard layer from the flat roof, because the chimney was resting on it, it's seems to be a single skin with no DPC and certainly no way for the water to exit. The pointing is a little suspect but I can't see how that alone could account for the amount of water entering the house, and logically with the way the roof has been constructed, effectively supporting the remaining stack I can't see how water ingress can be avoided. Perhaps the most telling symptom is the leak only occurs after several days of rain, not in storm force winds.

To put the chimney in perspective, it has already been lowered, capped and repointed about 4 years ago and before I bought the house the previous owners removed the ground floor section of the chimney, hence it cannot be used and why it rests on the flat roof, I'd anticipate maybe removing 2 bricks at the roof felt line or one course above to do each corner. Is there some part of the construction of the chimney that might cause problems using cavity trays and would I be better using DPC material and weep holes/vents?

thanks

mike

 

[AtoZ]

without seeing it, iwould think that your problem maybe a leak into the cavity rather than through the brickwork itself.
worth a look at the roof by the chimney because although you would solve the evident problem as you've described, your insulation will still be get wet and so wont be working worse still it will hold water like a poultice against your wall



cavity walls were made to repel water, it is a modern idea to fill it with insulation but that does sort of defeat the object of the cavity.

 

[mbuckhurst]

I think the problem is simply too much prevailing rain on rare occasions, we get water coming through maybe 2-3 times a year, when the weather is heavy continuous rain blowing against that particular face of the wall. What is noticeable is the bricks look sodden. If there's heavy rain against the wall/chimney for only a day or so, no matter how strong the wind or heavy the rain, we never see damp, it's these symptoms that made me suspect sodden bricks.

Due to the current work on the house, it's possible to see water dripping off the damp proof course that stops the sides of the windows bridging the cavity, and this always coincides with the water coming in the flat roof and chimney, and at this particular point, there is no doubt that the water is coming through the bricks or mortar joints, because there are no visible cracks in the mortar, whereas on the chimney the flat roof has settled slightly leaving a couple of mm of space.

I'd like to stop both problems, but due to the internal decorating, which includes a new kitchen I can't solve the first problem of water coming through the bricks, before solving the damp in the ceiling.

I'd be interested in suggestions for what to do to stop the moisture coming through in the first place? I've got some wall waterproofing compound for spraying a wall, but that can't be used until I guarantee several dry days, which is not easy in Manchester, but presumably there are other options? I guess I could replace the bricks with something more waterproof, but other than the expense, getting someone to do the work would prove difficult, hence I really need it to be a DIY exercise.

thanks

mike

 

[^woody^]

Has this stack been capped to prevent water getting down the flue?

I mentioned pointing, as soft mortar or mortar where the weathering as worn away, is the main source of water soaking into a wall.

Typically, it will only take a few hours for persistent rain to get through an external solid wall. Likewise, only hours for the wall to dry off.
Once it has permeated, it will run down and normally show itself within hours. Whilst not impossible, it would be rare for water to take days to drip out into the house. The wall retains moisture and it then evaporates, it does not constantly release the water once the rain has stopped.

So I wonder if there is water penetration elsewhere, leading to water accumulating and then traveling inside the structure? The flue or flat roof connection?

But checking/renewing the pointing and sealing the face of the wall will help if the wall is too porous.

 

[AtoZ]

Has this stack been capped to prevent water getting down the flue?

I mentioned pointing, as soft mortar or mortar where the weathering as worn away, is the main source of water soaking into a wall.

Typically, it will only take a few hours for persistent rain to get through an external solid wall. Likewise, only hours for the wall to dry off.
Once it has permeated, it will run down and normally show itself within hours. Whilst not impossible, it would be rare for water to take days to drip out into the house. The wall retains moisture and it then evaporates, it does not constantly release the water once the rain has stopped.

So I wonder if there is water penetration elsewhere, leading to water accumulating and then traveling inside the structure? The flue or flat roof connection?

But checking/renewing the pointing and sealing the face of the wall will help if the wall is too porous.

agreed.
the type of insulation might store/suck water but once bricks soak up a certain amount of water they cannot soak up anymore and shed the rest no matter how long it rains for. this is how concrete roof tiles work as opposed to clay.

i think you have a leak somewhere into the cavity. it maybe around the window..
i fixed a similar problem for a friend, they had had upvc fascias put on (cover type)
the fitters had just pushed up the plain tiles with the fascia till it fitted and then fitted guttering. the tiles now didnt all reach the guttering; allowing wind and capiliary action to drive water back on to the house.
it spalled the outside paint and some went inside the cavity where it collected by a lintel bearing.
when i lifted the tiles i could see the tracks of the water, plus i could see the dirt on the fascia.
i nearly missed it m8 and i was looking for the cause.

im hoping im right because it will be easier to solve long term than tompsons water seal

a cracked tile or slate could let this happen (it shouldnt but can and often does)


get yer ladder out m8 and buy the mrs some shoes with the money you save