Victorian ground floor flat - back to soil : which floor structure?

[cedrichn]

Good afternoon all,

Since a year now, we are proud(ish ) owners of a ground floor flat in a Victorian House in North London, with my fiancee. I am a mechanical engineer, enjoy working on my cars, but I am a real beginner for DIY inside a home Apologies for not using the correct terms...

The flat is a 2 bed, with damp in one bedroom. After removing all the layers in this bedroom (carpet, insulation, wooden boards, wooden beams, tarmac on tiles, small concrete-ish slab), I am back to the soil. I am now 99% sure that the humidity was due to the soil (or aggregate) being higher than the damp course in the walls (tiles): I can see the bricks under the tiles being humid, and the one above always dry. I now digged a lot out, and I wonder:
- How much deeper do I have to go?
- What layers/structure to go for? I read sand + modern DPC + concrete slab. Then, we would like wooden floorboards to match the corridor (all the flat is on suspended floorboards, except this bedroom)



Also, while digging, I found one rotten beam... I am not sure if it is the end of the beam holding the suspended floor from the corridor (on the right of the picture), or holding the internal wall, or a mix of both. I remove the crusty bits, and it looks like on the picture at the moment. What would you advise me to do with it?


Thanks for your help

Regards,
Cedric

 

[Cubist]

Hello and Welcome Cedrich.

Dont worry too much about the terminology, that will come in its own good time and we are all still learning about something - I hope.

First things first; the damp beam needs investigation as it could spell trouble. In your last picture I see a section of a joist carrying a timber floor in an adjacent room or corridor. Is the damp you are seeing on this or on another timber attached to the joist? Can you supply a picture of the damp you are seeing and have you any ideas where the damp may be coming from?

Have you any idea what the white plastic pipe coming up through the floor if for or when/why it was installed?

Others who have done similar work will soon offer their opinions concerning whether you need to excavate any more earth and how best to re-establish a floor in this room. Personally I would favour a suspended timber a floor mounted on a framework of joists in pretty much the pattern of those you have removed - and this approach may mean that you do not need to put any material over the exposed earth.

Cheers for now,
Cubist

 

[Toby Newell]

Hi

I defer to experts in construction and damp, I'm basically a wood restorer with ridiculous mission creep.

I have rebuilt floors from the earth up.

First of all make sure you have checked for other causes of damp.

I would excavate to the same depth as the rest of your property.

Then copy what already have, which I presume is pier = dwarf = small supporting walls.

You will need to bed these in mortar, leave gaps in the wall for ventillation.

When fitting joists over the top we put a roll of pvc dpm underneath the mortar bed.

I guess it would do no harm to put a layer of slate somewhere after the first couple of courses (layers) but we didn't.

A concrete slab is expensive and rather silly, you might end up where you were before.

A 6 inch concrete slab can also take 6 months to dry out before you can lay timber on it.

PS where are you in N London? I lived and worked there for most of my life. (You might have spotted the builder depot bags...)


PS The below was a houae near Wimbledon, some previous geniuses had poured several tons of concrete in the adjacent narrow garden return, for reasons only comprehendable by superior intellects. It was removed. I initially was going to sand the boards but after I started I realised the floor was rotten down to and including the brick dwarf walls. The photos are downloaded via mobile from my website home page. When I get back from working away I will post the photos of the seat beam I took out, for fun! in some places it was a 3mm empty shell!

and FYI I am neither a carpenter nor builder, just a French polisher (who studied engineering) who got too carried away.

I'm basically an amateur with a peverted reluctance to say no. If I can do it, you can.

 

[cedrichn]

Thank you both for your fast feedback!

Cubist, with another picture, it will be easy to explain all the pipes and cables According to the upstair neighbour who lives here since few decades, we have "recent" floorboards. I guess they installed new plastic pipes for the central heating at the same time ("sadly").
I can't really find any damp where the beam rot. The damp in this room was along the external wall, where the soil and/or aggregate was higher than the tiles acting as DPC on the brickwork. The plastic pipes for heating and bathroom next door are suspect, but all look dry from what I can see...
- You think I should try to change the beam?

Toby, this looks impressive! I am in Bounds Green I don't know what are the rules of the forum around suggesting people, but if you can recommend any builder, I am all ears I am not OCD, at all, but I find it really difficult to find people who cares about doing their best, and know what they are doing. Hence why I came here: to know and understand better

To both, I see that you are both pushing for suspended floor... What pushed me out of it is - that is going to make me look lazy - is the amount of soil I have to remove... Secondary reasons are: I read that you need to lay a slab to prevent "animal ingress by tunnelling", I have no ventilation to the outside in the external wall, and it looks more complicated than laying/pooring floor

But, I came here ready to change my view, and understanding what is the best

For suspended floor, is it that you can have two designs ? either dwarf walls, or beam embedded/integrated into the side walls using joists?


(above picture show that the aggregate/soil was higher than the tiles in the brick wall)


(North is where you can see the black spiral on the top of the page, which make the external wall facing North and being more sensitive to humidity)

 

[cedrichn]

Maybe this answers a few of my questions: use joist hangers on the brick walls, and how to replace rotten ends

How to Use Joist Hangers

Learn about how to use joist hangers or jiffy hangers and how they are used to install floor and ceiling joists that are sturdy and strong

www.diydoctor.org.uk

 

[Toby Newell]

Hi

My daughter lives opposite Colney hatch lane Tescos in my flat and I lived at 32A Bounds Green Road for a few years! (brought up in Crouch end)

I know someone opposite Compton School on Summers Lane in Friern Barnet but due to Covid his guys haven't returned back to the UK yet, I will message him and ask if anything has changed.

Sorry, I don't know much about hangers, depends how strong your bricks and mortar are. Earth is more of a known quantity, good old action and reaction. Your bricks don't look too fantastic tbh. I would dig and do walls myself, yes hamgers are strong and so are concrete screws, but they are only as strong as the substrate you are drilling in to.

Never heard of the animal tunneling, sounds like a rodent phobics peverse fantasy, there are millions of rats in London and Bounds Green has tons of fast food restaurants, no idea why they would waste time tunnelling into a dark, damp, empty void when there are hundreds of wheelie bin condos with free food service. Mice can simply slip through cracks the width of a medium sized sharpie, seems like twoddle to me.

I would replace the rotten timber with C24 pressure treated with pvc roll underneath or bitumen dpc paint, you can add extra cancer fluid, sorry, wood preservative if you like.

Pouring concrete is generally a bad move in any period property, especially if that is not how it was designed, deffo go for the suspended floor, it really does take around one month per inch to dry too.

You don't really have an excuse, I think the Southgate Builder Depot might be the largest in the UK and it 's 5 minutes drive from you!

 

[Toby Newell]

Maybe this answers a few of my questions: use joist hangers on the brick walls, and how to replace rotten ends

How to Use Joist Hangers

Learn about how to use joist hangers or jiffy hangers and how they are used to install floor and ceiling joists that are sturdy and strong

www.diydoctor.org.uk

FYI

Always qualify your.advisors.

Quite a lot of adverts on the page, including 'if you don't fancy doing it yourself, click here.'

It's a sham site, just regurgitating info from Wikipedia (frequently innaccurate) and other stuff.

Having written and published multiple websites and several hundred thousand word articles, I have done a lot of research, reading and watching what amounts to an incredible amount of bollocks.

Rotten ends? currently conserving a large 1450 cottage, resin lol. Hyper bollocks. Remove and replace and scarf in supporting with either metal plates either side or sistered joist with 50% overlap using M16 or M12 coach bolts, depending upon span, and square washers. Put your engineers head on! Butt joint with holes drilled in? Brilliant.

Have you checked out Mike the DIY doctor and "industry expert in building technology"?

His Linkedn page says he likes golf courses and has a degree in Marketing.

He may indeed be an expert in building technology but let us be logical. If he is such a marketing expert with so many marketing skills...

Would he not update his Linkedn page with some of his building and engineering skills and experience? And if he hasn't then he is obviously crap at marketing, which appears to be his main thing.

Which makes me somehow doubt the brilliance of his building technology skills

Maybe extend your search for relevant advice.

Don't feel bad, the internet is 49% porn, 25% cats being silly, 25% bullshit and 1% accurate information. Divining the 1% is an art and a skill they should teach in schools.
'

 

[Cubist]

Hi Cedrich,
Thank you for the additional information and particularlly your sketch of the layout of your flat. To focus on your problems and opportunities: -

1. I believe your priority should be focused on the beam in which you have observed some rot. The beam is clearly load bearing as it carries the partition wall between the bedroom and bathroom in your flat and 'may' also carry the weight of a similar wall in the flat above your own.
   1. It is vitally important that you understand the extent of any decay to this timber to help define a best treatment plan.
   2. Please supply a photograph of the damage you have found and indicate the extent of the rot/decay.
2. A portland concrete floor will only add to the damp problems as any moisture coming up through the earth will be driven toward the walls.
3. A limecrete floor would be possible and would be breathable but as with portland concrete there are significant issues concerning how much you might need, how and where it would be mixed, etc. Frankly I would suggest that, for you, concrete/limecrete floors would be a needless waste.
4. Burrowing animals in urban areas are usually restricted to those that depend on the food waste we humans produce and leave lying around. All of them will stay very close to these food sources and will make their nests nearby. Bluntly, you, and your neighbours, should not worry about these beyond making sure that your domestic waste is properly stored and disposed of.
5. Joist hangers may very well be your best solution to support a new array of joists to support a wooden floor. But, successful use of these will depend on the the stability and strength of the timbers and/or brickwork on which they are mounted. A key priority for you right now should be to stabilse and strengthen the brickwork and timber.

Cheers for now,
Cubist

 

[Drayton]

Given the bathroom is the other side of the wall, is there any plumbing close to the section of the beam that is rotting?