Cavity walls construction

[ant3000]

I’m looking for a little advice re; the construction of mine and my neighbours terrace of houses. In the last year or so we’ve started to suspect that rats have accessed our cavity walls and are moving between the properties.

We have each noticed burrow holes coming out from close to the external walls and so have dug down a little and now believe that the foundations may be suspended block and beam meaning there is a cavity running underneath all of the properties in which the rats have started to nest (possibly gaining access via damaged drainage).

Where we have dug we have discovered that drainage lintels run at sections along most of the front wall and can see the cavity runs right under the houses. We’ve been able to photograph up into the cavity wall and this appears to be completely open at the bottom and we can see the air brick housing and damp course. Is this considered to be ok? Should a “cavity tray’ been fitted above any exposed areas of the cavity wall?

It just seems to be an open door to pests?

Any advice would be much appreciated.

 

[noseall]

There appears to be a lintel (over a drain etc) in the image. Its a difficult one to manage in terms of building rules and reg's. There needs to be a clearance above and around the lintel to protect the drain with little regard for vermin access.
You need to dig around and below the lintel to fully expose the bridged gap and look how to block up the hole without compromising the pipe beneath.

 

[ant3000]

Should a cavity tray have been fitted above the drainage access but below the damp proof course?

My concern is that the cavity wall hasn’t been filled below the DCP throughout the walls? Is this conceivable?

 

[noseall]

Should a cavity tray have been fitted above the drainage access but below the damp proof course?

Possibly, or some kind of shuttering or packed with insulation.

My concern is that the cavity wall hasn’t been filled below the DCP throughout the walls? Is this conceivable?

Strange that none of it is filled, very odd. It does get tricky trying to maintain clearance around passing sewer pipes whilst attempting to fill the cavities above them, but this should not affect the rest of the build in terms of filling.​

 

[ant3000]

I’ll have a dig past the drainage opening and see if I can get another pic

 

[^woody^]

Should a cavity tray have been fitted above the drainage access but below the damp proof course?QUOTE]
No. Thats not what cavity trays are for.

Rats gnaw through DPC anyway.

 

[ant3000]

It seems that might be the case which is why I figured they should have blocked access below the dpc

 

[^woody^]

It's difficult to see what's going on there, but in general terms, cavities should be filled up to around 225mm below ground level. When pipes are close to this level it can be awkward as pipes require some space around them in case the building moves, so yes there are times when the cavity is just left open above and around the pipe.

If that's a route in, then you need to block the cavities with some stainless steel mesh scrumpled up to wedge in, and form a barrier. You can also afford to infill with some lean concrete to close up any large voids, and put the mesh around the pipe in a 50mm or so perimeter