Where is the DPC line

[denvysb]

Hello all. My first post but have been browsing the site for years.

Intended to pave out the little front terrace but for the life of me can not figure out where the DPC line is so I can build it 150mm below it. It is a property built in the 1920's with a cavity wall.

I've dug out patches of soil expecting to find a visible dpc line, slate or different coloured bricks but so far don't see anything that resembles a DPC line.

Does anybody know based on the picture and age of the property where the DPC line would be?

 

[JohnD]

The DPC might be easier to see beside or under the doorstep

Are you on a hill?

Stand back and take a wider pic. Clean out some of the mortar joints with a hose so you can look inside. It might be immediately under or above the airbricks.

Looking at the bricks, the lowest ones seem to have lime bloom that does not seem to show on the course above, so it might be the dpc is between them. Are any of the bricks very hard and shiny? Are you anywhere near a canal to Accrington?

 

[denvysb]

Hi John. Thanks for the reply. Yes I'm on a hill and under the doorstep I can see the bricks are a different colour than the bay window. Theres a single row of yellow bricks under the doorstep. Would that be the DPC line?

 

[JohnD]

More pics please

 

[denvysb]

Got late last night but here are some more pics.

 

[JohnD]

I can't see it, but I think your existing concrete path is already too high. This is a very common mistake. I think it is flush with an old stone step, so the original ground level will have been around ten inches lower. The mortar joint fractionally above the path may be a little thicker than the others, and looks long-term damp, from the colour, the vegetation, and I think I can see a drill mark where a futile attempt to use silicone injections has been made. So I think you need to dig out another foot, and hose out the mortar joints. Old lime mortar is prone to wash away over time if it is wet, and needs repointing.

It's possible, but IMO unlikely, that your house was built without a DPC. In London they were compulsory from 1875. There were regional variations but your house build looks quite ordinary. The quality of the original brickwork on the front elevation looks high.

The air bricks do not look original to me, I think they were an attempt to reduce a long term damp problem. Have a look under the floor. Plot the route of the incoming water supply pipe, which will often start leaking when 60 to 100 years old. It may run under the hall floor. If you are on a slope the source of water may be running down. Do you have a water meter?

Look for any source of water encouraging that lush vegetation, such as a gutter, porch roof or downpipe. The roofs and gutters on bay windows are often in poor condition. The stone (?) wall between the front door and the bay looks dark, as if there is water coming from above

Some of your neighbours with similar houses may show the original ground level, or an old path. Or old drains, gullies and manholes will show it, though if they have been leaking they may have settled into the ground or had concrete incorrectly laid round them.

Under no circumstances allow anybody who sells silicone injections near your house.

 

[George_engineer]

If you can't identify it, going for 150mm below internal floor level should be fine.

 

[denvysb]

Thanks Johnd. I've had a look around a lot of the neighbours houses and they all seem to have this one course brick under their doorstep and then a ramp path leading to the pavement.

It was a house owned by a couple that lived aboard that was rented out. They had never visited for 20 years and the house was in a state. I'm now picking up all the things that need fixing.

So how low would you suggest the new patio levels up to the front bay bricks?

 

[JohnD]

I think you should dig against the house wall until you can work out where the original gound level used to be, and lay your new paving to match. While digging, look for any broken drains or leaking pipes. If you find the footings are very shallow, you can dig out short stretches and pour concrete.

I think there is an extra problem, looking at the vegetation growing in the wall, that there is a source of water, likely a leak, that needs to be repaired.

Additionally, the brickwork needs the joints washed out and repaired. You can clean out the dirt and perished mortar with a strong hose, but the brickwork is very fine and deserves a skilled and careful workman to restore its original beauty. To my eye the joints look too narrow to use a pointing gun, and lime mortar is preferred as original. I would use cement mortar below the DPC (if you can find it) as it is more durable when wet.

Where I come from old yellow bricks are somewhat inferior, soft, made from river mud, and not much used for strong or showy work, but used on the sides and backs of houses. The light bricks beside your front door are much better. The red bricks of your bay were chosen to impress.

If you want to teach yourself pointing, start at the back of the house where I bet the brickwork will not be so fine (on the popular Victorian "fur coat and no knickers" principle)

 

[denvysb]

Thanks John. For that kind of work I'm likely to hire someone to do all the pointing work. Indeed your correct there were several leaks from the old top guttering, paid to get that sorted recently. Touch wood all the leaks appear to have stopped but need to clear all the vegetation.

Now trying to sort out that little front bay patch. Just wish the DPC level was obvious so that I could just crack on with levelling it out.

Thanks for your help so far

 

[Loofah]

I'd say it was here -

 

[JohnD]

May well be. Or the joint above where the lime bloom abruptly stops. Give it a squirt with a jet washer, or a nylon brush.

 

[tell80]

OP,
Use a very thin broad blade screwdriver to scrape a few mm's out each mortar bed until you hit a bed with some kind of a DPC.
A 1920's build will usually have had a DPC of some sort of material
Do you have any internal indications of damp on the front walls?
If its possible, It might benefit you to crawl under the suspended floor, & examine any joist tails sitting in brick pockets in the front wall - probe the joist tails for rot. Check that the air brick ventilation continues thro the inner skin?

 

[denvysb]

Thanks all. Waiting for a dry day to start investigating. What should I be expecting whilst taking few mm's out?

Am I looking to hit some sort of solid black slate behind the mortar?

@tell80 there are small damp patches on the front internal walls but I think it's due to condensation because it appears in the same places in the room above. Always in the Corners. The recent cold spell I measured the temps. The internal bay window was (3-4°) whilst the outside temp was (0°), always a 3-4° difference at any given time. But the internal room temps were far higher at (16-17°), could be wrong but that's usually a perfect environment for condensation to build. During hotter temp damp disappears.

 

[noseall]

The (official) DPC will be directly above the airbricks. There will also be a subsidiary internal course DPC below the timber floor joists, sitting two courses lower than the (official) DPC. However, it also can depend upon how the builders foresaw external ground levels in relation to floor joist height positioning as to whether they kept internal and external DPC positions the same. A lot of these timber floor houses had a large step up into the property hence the lower (beneath the joist) position of the DPC, inside AND out.