DPC and footings only 1 row apart

[jconnolly]

Hi, first time poster, long time reader . I live in a Victorian 3 bed terrace, built in 1895. Yesterday I started reducing the external ground level and taking off a cement plinth around the rear side of the property, where the main body of the house (dining room) meets the rear part of the house (kitchen). Both of these rooms have blown plaster internally along these walls and I get high humidity readings. I uncovered what I am guessing is a bitumen DPC under the plinth, and a soil blocked airbrick which was below the paving level (internally this airbrick sits behind the skirting board above a suspended floor). The DPC is directly below the airbrick (meaning internally it's at floorboard level). I made, what I thought, was good progress along the main body of the house digging out two rows of bricks below the DPC (on this wall there are 3 rows below the DPC before the footings start). and removing the cement plinth (although the faces of the soft red bricks also came away). However, when I got onto the rear part of the house I found the footings only 1 row of bricks below the DPC. From my understanding the DPC should be at least 2 rows of bricks above ground level, and the footings should be at least 1 row of bricks below ground level. Obviously both of these things can't be achieved with only 1 row separating them, but the question is what to do? I can't get my head around how this would have been originally. The airbrick and DPC would surely have been above ground? But does that mean the footings on the rear would have been exposed? Any advice would be appreciated!

 

[Zebra]

Sorry, don't understand the question!

 

[jconnolly]

The question is, given that the dpc is only 75mm above the start of the kitchen foundations, where do I reduce the ground level to?

 

[erikwoolf]

Hi, first time poster, long time reader . I live in a Victorian 3 bed terrace, built in 1895. Yesterday I started reducing the external ground level and taking off a cement plinth around the rear side of the property, where the main body of the house (dining room) meets the rear part of the house (kitchen). Both of these rooms have blown plaster internally along these walls and I get high humidity readings. I uncovered what I am guessing is a bitumen DPC under the plinth, and a soil blocked airbrick which was below the paving level (internally this airbrick sits behind the skirting board above a suspended floor). The DPC is directly below the airbrick (meaning internally it's at floorboard level). I made, what I thought, was good progress along the main body of the house digging out two rows of bricks below the DPC (on this wall there are 3 rows below the DPC before the footings start). and removing the cement plinth (although the faces of the soft red bricks also came away). However, when I got onto the rear part of the house I found the footings only 1 row of bricks below the DPC. From my understanding the DPC should be at least 2 rows of bricks above ground level, and the footings should be at least 1 row of bricks below ground level. Obviously both of these things can't be achieved with only 1 row separating them, but the question is what to do? I can't get my head around how this would have been originally. The airbrick and DPC would surely have been above ground? But does that mean the footings on the rear would have been exposed? Any advice would be appreciated!

View attachment 11864
View attachment 11865

We had the same issue, property build around 1860s, 1 brick course between DPC and footings. Our structural engineer advised not to expose the footings so we had to compromise (the property is 4 stories high!). We resulted with the ground level just one course below the DPC and a slot drain along the wall. We get a little bit of splash back when it rains but inside we plastered with lime and for the moment it seems to work OK. We actually used Diathonite in the worst areas affected by damp and so far looks great. Obviously we are at the start of the winter so will have to see how it goes.

 

[paulc]

Likewise, same issue here with a 1920s semi. If I dig down 150mm, I expose the top of the foundations. Ended up going down as far as I dare, and created a trench 200mm wide which is filled with a decorative gravel. At 75mm below the DPC, the wall remains fairly dry, and no sign of penetrating damp internally.
The 150mm you hear quoted is "best practice", and it is accepted that this is not always achievable when renovating. So you can only go so far and use other measures in mitigation.

 

[Zebra]

The question is, given that the dpc is only 75mm above the start of the kitchen foundations, where do I reduce the ground level to?

It's OK to expose the foundations, from a structural point of view at least. It's OK to expose right down to the bottom of the lowest foundation course, and if necessary, it's OK to dig a 45 degree slope away from the foundation course in order to go even lower.
Ideally you'd expose 150mm below DPC, but anything is better than nothing, and if there is a greater height exposed elsewhere around the house, then a lesser height exposed for a short distance will not pose a problem.

 

[jconnolly]

Thanks all! @erikwoolf @paulc it's encouraging to hear you've had some success with only one course gap between the dpc. @Zebra interesting to know about the structural integrity. Is another reason you may want the footings covered greater resistance to frost damage? If so, is there any way to increase resistance where they are exposed or have minimal coverage? It is a fairly limited length that has these shallow footings where I'm reducing the ground level (~4 meters along the kitchen wall), so again that's encouraging to hear.

 

[Zebra]

The only reason footings would be more susceptible to frost damage than other brickwork is because they're wetter, and spalling can ensue when moisture is trapped in bricks, but if moisture can evaporate then they'll be fine.

 

[stuart45]

The main problem is frost heave. It depends on the soil type. Chalk can be a problem, as well as certain clays.

 

[Culturealgap]

Hi, first time poster, long time reader . I live in a Victorian 3 bed terrace, built in 1895. Yesterday I started reducing the external ground level and taking off a cement plinth around the rear side of the property, where the main body of the house (dining room) meets the rear part of the house (kitchen). Both of these rooms have blown plaster internally along these walls and I get high humidity readings. I uncovered what I am guessing is a bitumen DPC under the plinth, and a soil blocked airbrick which was below the paving level (internally this airbrick sits behind the skirting board above a suspended floor). The DPC is directly below the airbrick (meaning internally it's at floorboard level). I made, what I thought, was good progress along the main body of the house digging out two rows of bricks below the DPC (on this wall there are 3 rows below the DPC before the footings start). and removing the cement plinth (although the faces of the soft red bricks also came away). However, when I got onto the rear part of the house I found the footings only 1 row of bricks below the DPC. From my understanding the DPC should be at least 2 rows of bricks above ground level, and the footings should be at least 1 row of bricks below ground level. Obviously both of these things can't be achieved with only 1 row separating them, but the question is what to do? I can't get my head around how this would have been originally. The airbrick and DPC would surely have been above ground? But does that mean the footings on the rear would have been exposed? Any advice would be appreciated!

View attachment 11864




View attachment 11865

If it's possible, try to reface the bricks to make the surface as flat as possible, to avoid damp hiding in the irregular surface. Rough surfaces containing moisture can result in frost attacking the surface.
Brick firing kilns have two or more grades of brick. The tunnel kilns are more or less self firing: the clay contains burnable content, but the bricks closet to the outer cumference don't get as hot as those closet to the centre. The softer bricks were used for internal cross-walling and partitions. Some builders, to save money often used the soft brick on exterior walls, which can't resist the weather.
(Some modern builders, who buy reclaimed brick, don't realize that the yards indiscriminately mix the salvaged bricks, resulting in a mix of brick being used in the "quaint" new housing estates!!)
Back to damp.
Another aspect is correct pointing. The pointing in your images isn't right. Most DIYers don't know about pointing irons, which come in various sizes: 1/4 inch upwards.

They are the same shape as normal trowels and fit into the binder seams creating a recessed flat surface. The surface should be of a depth equal to the width of the seam. Sloping pointing is incorrect, as is flushed pointing.

A Swiss navel officer, in the early 20th c invented a system of incerting porous terracotta tubes into damp walls which allowed moisture to escape. I was told this by John McClane Thompson, Emeritus Prof at Liverpool University, in the 70s.

Rising damp rarely goes higher than one metre, and depending on the thickness of the wall can be solved quite easily.

I live in a building with 24+ inch rubble-stone walls using limestone field-stones and primitive terracotta clay, as binder, so I can easily fight the moisture.
I developed a system for thin walls, which involved using a dado system. This involved placing a top quality plastic sheeting behind the dado paneling, which is tucked back under the wall.

This allows the moisture to condense on the plastic and return to where it came from!
I've encountered the use of bitumen DPCs from the turn of the 20th c. They most probably failed not long after being installed depending on the weight of the masonry.
When pointing with lime, try to use hydraulic lime, and only use that with NHL, (HL and FL limes have added cement) NHL 3.5 or NHL 2 are OK. NHL 5 is for supports. It also has a greyish tone, which doesn't look good.

Enough for the moment

 

[jconnolly]

@Zebra @Stuart X-Ray thanks, that is reassuring!

@Culturealgap very interesting info on the bricks, thanks! I've also been told that applying a lime wash to them (instead of repairing/replacing) is a good idea to add some protection against water, do you think that's a valid alternative? You're right, the pointing on the entire back of the house is horrible, thick cement that has been there for at least 30 years, is well bound, and takes off the edges of the bricks when removed. My plan is to rake out ~1.5m closest to ground level this winter, and repoint with lime in the spring.

 

[sarah.in.liverpool]

@Zebra @Stuart X-Ray thanks, that is reassuring!

@Culturealgap very interesting info on the bricks, thanks! I've also been told that applying a lime wash to them (instead of repairing/replacing) is a good idea to add some protection against water, do you think that's a valid alternative? You're right, the pointing on the entire back of the house is horrible, thick cement that has been there for at least 30 years, is well bound, and takes off the edges of the bricks when removed. My plan is to rake out ~1.5m closest to ground level this winter, and repoint with lime in the spring.

Hello jconnolly, how are you on your journey now? Have you limewashed the bricks? Is the top of the foundation footing still exposed?

I'm in a similar situation to you and wondering on what's best to do next.

 

[jconnolly]

@sarah.in.liverpool Hi - I finished off removing the cement plinth and digging the trench, leaving it at the same height as the top of the footings. Then I've just left it for the last 9 months, partly just to see what happened, but mainly as other jobs have taken priority. Wall is dry and functioning well, even after an incredibly wet 9 months. No issues whatsoever. My plan is to dig a little deeper exposing the top of the footings along the kitchen wall, add a layer of largish round stones over the top, and limewash the brick where the plinth was removed. Somebody from building control came around for another job, and agreed with Zebra that exposing the top of the foundations would not be an issue.

 

[sarah.in.liverpool]

@sarah.in.liverpool Hi - I finished off removing the cement plinth and digging the trench, leaving it at the same height as the top of the footings. Then I've just left it for the last 9 months, partly just to see what happened, but mainly as other jobs have taken priority. Wall is dry and functioning well, even after an incredibly wet 9 months. No issues whatsoever. My plan is to dig a little deeper exposing the top of the footings along the kitchen wall, add a layer of largish round stones over the top, and limewash the brick where the plinth was removed. Somebody from building control came around for another job, and agreed with Zebra that exposing the top of the foundations would not be an issue.

Thank you @jconnolly ! That's much appreciated.

I'm now planning on laying quarry tiles in the side return. In a dry mix of NHL and sharp sand? Big gaps in-between. With a line of gravel over the top of one footing of the house and the footing of the garden wall.

Hope this works!