How to close cavity when using lintels above sewer?

[ChrisZx]

We've got to lintel over a sewer at foundation level, so one lintel under each skin. How do you close the bottom of the cavity?

We haven't dug out around the sewer so it will be sitting just above the earth unless we do anything else. Surely over time it would just fill up with rubbish and start touching the cavity insulation, leading to damp?

What do people normally do with this? Couldn't seem to find any info

 

[WabbitPoo]

Where's all this "rubbish" going to come from?

 

[garyo]

I filled my last with enough pea shingle to get it to lintel level then chucked all my left over mortar on it over the next few days so it formed a solid closure even if the pea shingle settled eventually.

 

[noseall]

Use a piece of we'll packed cavity wall slab insulation as protection over the pipe prior to filling the cavity with lean mix.

 

[ChrisZx]

Use a piece of we'll packed cavity wall slab insulation as protection over the pipe prior to filling the cavity with lean mix.

Thanks but that's not really my situation, the pipe is buried 1.5m below the ground! We're lintelling over the gap we left (and didn't dig out) for it, so the question is how to seal the bottom of the cavity over the gap.

Wondering if it might be easiest to put another lintel in-between the two lintels for the skins... a 100x65 lintel will hardly cost much. Think we only need 75mm of cavity fill at the bottom but would make it easy to do so

 

[^woody^]

If the pipe is 1.5 m below ground, then surely you are filling the cavity with a concrete and so nose's post does describe your situation.

 

[ChrisZx]

The pipe is 1.5m below ground with 1.5m of undisturbed earth above it so doesn't need any additional protection which I think is what he was getting at?

I'm clearly not explaining this very well... my problem is that there won't be a bottom to the cavity as we lintel over the two foundations either side of the sewer. There will be a lintel under each skin of wall obviously but nothing between them, and I'm assuming I should do something to stop stuff getting up inside the cavity from below, as the opening sits below the external ground level because it's right on top of the foundations. Any clearer?

 

[^woody^]

The pipe is 1.5m below ground with 1.5m of undisturbed earth above it so doesn't need any additional protection which I think is what he was getting at?

I'm clearly not explaining this very well... my problem is that there won't be a bottom to the cavity as we lintel over the two foundations either side of the sewer. There will be a lintel under each skin of wall obviously but nothing between them, and I'm assuming I should do something to stop stuff getting up inside the cavity from below, as the opening sits below the external ground level because it's right on top of the foundations. Any clearer?

If the pipe is 1.5m below ground, and you are lintelling over it, then surely you have 1.5m of cavity wall above it.

You can't be saying that the pipe is 1.5m below ground with undisturbed earth and then you are starting the cavity wall? That would be bonkers.

 

[garyo]

That's how I read it now - Chris has effectively created two pad foundations and is asking how to build a wall between the two? How wide is the gap? can you use three lintels?

 

[garyo]

I'd have dug down and done it at a lower level so that you have a continuous run of foundation so that theres no chance if differential movement in the two sides of wall.

 

[ChrisZx]

Yea that's basically it. I just pulled this image from the internet but it's similar to what we're doing.

I have seen people question movement between the two foundations so did wonder, but BCO didn't have a problem with it so that's what we went with.

I think an extra lintel is going to be the easiest way.

 

[pilsbury]

When I built my cavity wall over my drains, I bridged the gap with 3 65x100 lintels next to each other. 1 for each skin and 1 for the middle. Then my lean mix below DPC sat all nicely on this middle lintel.

 

[^woody^]

Wtf.

For sanity reasons I've been forced to start the bank holiday drinking early. Perhaps things will be much clearer later. Perhaps.

 

[pilsbury]

For sanity reasons I've been forced to start the bank holiday drinking early.

Any excuse.

 

[tomfe]

Cavity batt sits on wall ties, are you sure you're just not inventing a problem.