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Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Mon, 23 Feb 2009 09:26:31 +0000

Posted By: ali.gillDont forget air bricks within the sleeper wall for cross ventilation, and also a DPC.

Sure thing. My plan to support the joists is:

timber on mortar on DPC on mortar on single layer of bricks on concrete strip foundation.

The single layer of bricks will have gaps between the bricks to allow cross ventilation

Ground floor joists touch the soil - is this a problem???

ali.gill — Sun, 22 Feb 2009 14:25:55 +0000

Dont forget air bricks within the sleeper wall for cross ventilation, and also a DPC.
When exposing the rotten joists stick photos up of the damage - real close to the timber -

Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Sun, 22 Feb 2009 08:28:44 +0000

Thanks for all the replies.

I've spoken to our local BCO and I've sent him my plans. I'm going to rebuild a wooden floor with sleeper walls which are 1 brick high. I'm going to add 4 air bricks to the external wall to ventilate the underfloor space. And I'm going to install 120mm phenolic insulation under the underfloor heating.

Also (I didn't tell the BCO this) I want to run a bunch of 1-wire sensors down there to measure temps and moisture.

Regarding the possibility that our floor was originally paved compacted earth... this is an intriguing possibility but I think it's unlikely in our case because the internal masonry wall seems to have been built on top of the floor boards, suggesting that the wooden floor has always been there. I could be wrong though.

Thanks loads for all the help,
Jack

Ground floor joists touch the soil - is this a problem???

chuckey — Fri, 20 Feb 2009 17:22:04 +0000

Dan I think you missed my point. sleeper walls are built to equalise the ground slope/housing levels over a whole site. My house has a void of 5' under one end of it and 18" under the other. this variable distance is made up by the sleeper walls. The sleeper walls only stand on strip foundations. My method is essentialy the sleeper wall system without the bricks and no bearer on top of them. As your floor has other then the rot managed to remain flat when the weight of your contents was bearing on the 2" bit of the joists, putting this on a narrow paving stone to spread the width to 9" or more will not weaken anything. The only issue is is there sufficient room for ventilation? = height of paving stone*, I would think so. To insulate, nail netting to sides of joist, put battens on top of DPC, giving you some surface to put your insulation on.
* you could always run two courses of paving stones , like bricks to give 9" bearing width and increased headroom for insulation.
The enormous advantage is that you can do it your self or with a friend, over a weekend or a strip per evening.
Frank

Ground floor joists touch the soil - is this a problem???

martint — Fri, 20 Feb 2009 12:43:09 +0000

I used to live in a terraced house in Staffs which had an earth floor, with tiles on top. Amazingly, we did not have any damp problems! It could be that your house was similar, and what you have is someone's attempt to create a wooden floor, by digging out a few inches of earth, and sitting 'joists' on top of the earth. If this is the case, then structurally you would probably not be able to get the depth to replace with proper joists, with the necessary depth and clearance. (Our foundations were fairly shallow, on clay).

Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Mon, 16 Feb 2009 15:20:18 +0000

Just a quick update.

I've been considering our options for rebuilding our floor. The options seem to be:

1) Rebuild a suspended timber floor
2) build a concrete solid floor
3) build a limecrete solid floor.

Concrete is out because it would be impermeable and hence would force moisture into the walls (plus we have concerns about the embedded energy of the cement)

Limecrete is out because we'd need 350mm of LECA plus 100mm of LECA+limecrete to achieve a U-value which satisfies building regs. Not only would this depth of material require us to excavate below our foundations but it would also cost over £3,000 just for the LECA and NHL.

So... the conclusion is that I should rebuild the suspended timber floor. The joists will be completely supported by sleeper walls. I'll probably use 4 sleeper walls which will result in a max span of 2.3m so I think I can use 70x145mm joists from our local timber merchant (total cost of 48m of wood for the joists = £198).

There is only a single air brick in the floor at the moment so I need to add some more air bricks to ventilate the underfloor space.

I'm planning to put some drawings together to send off to the Building Control Officer (along with drawings for the insulation for the rest of the house, even though I wont get round to that for 12 months or so).

Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Tue, 10 Feb 2009 08:32:01 +0000

Many thanks, you've cheered me up no end! I'll stay calm and carry on!

Ground floor joists touch the soil - is this a problem???

ali.gill — Tue, 10 Feb 2009 01:34:26 +0000

Stop whingeing.. i've got a whole house to rebuild, along with an office and woodshed to build with about �12.78 i found down the back of the sofa. I will not allow these negative comments on the glorious gbf and banish them forthwith.

You have uncovered timber decay before it has taken hold and caused the floor to sink beneath you, so glory in your findings and the potential future cost you have saved yourself.
A crumbly joist is something we all have somewhere, except , its just that you know where yours is.
Its possible that you dont have penetrating damp through the masonry but that condensation formed on the cement coat and ran down to meet the joist, mated and gave birth to Rotius McWoodcrumble.

I was really excited by the "superjoist" and then deflated by the thought of cuddling a bco or finding a 'stool' under the floor. Tony please refrain, god only knows what would have happened if i'd been eating a cadburys mini roll at the time of reading that word.

Ground floor joists touch the soil - is this a problem???

tony — Mon, 09 Feb 2009 23:12:15 +0000

The "superjoists could be on short brick stools. try looking about half way down their length. Do they go into the wall or do they sit on a stool at the ends?

Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Mon, 09 Feb 2009 21:26:27 +0000

OK, I've finally gotten round to doing a more thorough exploration of what lies beneath my floor. It's not great news.

The joist nearest to the external wall is completely rotten. It crumbles in my hand.

The joists are supported by perpendicular wooden "superjoists" but I haven't yet figured out what supports the "superjoists". I fear they are just resting on the ground. There's no evidence of any brick work beneath the superjoists or any DPM separating the superjoist from the ground. One half of one of the superjoists I've uncovered is completely rotten.

I've attempted to find how deep the foundations are. The exploratory hole I dug suggests that the foundations finish 390mm below the bottom of the existing floor level! The foundations seems to consist of a "brick footing" which rests directly on the clay. There is no sign of there being any concrete at the base of the foundations. This type of foundataion was apparently not too uncommon in houses built when my house was built:

http://environment.uwe.ac.uk/video/cd_new_demo/conweb/house_ages/elements/section1.htm

I'm also yet to find any evidence of a DPM in the external wall. I have found evidence that the interior face of the external wall has had waterproof concrete applied, supposedly to reduce the penetration of damp into the internal face of the external wall.

I haven't yet figured out exactly where the external ground level is relative to the inside of the house. I'll try to figure this out ASAP.

I'll keep exploring. It's all rather worrying.

Part of me wants to cuddle up to our local building control officer to find out what they think but part of me is terrified that they will demand that we commence hugely expensive work. Sure, the building might need a set of expensive fixes (underpinning the foundations, digging down the external ground level, retrofitting a DPM, re-building the entire ground floor...) but I just don't have the cash! Tricky...

Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Thu, 15 Jan 2009 12:18:46 +0000

Thanks loads for all the replies.

I must admit that I haven't yet gotten round to pulling up any more floor boards to find out what's down there but I will do so soon.

I think I will go for the "new timber suspended floor" option rather than pooring tonnes of concrete into the hole.

Instead of going to the huge expense and effort of installing underfloor heating, I will stick with my two radiators but I will take the opportunity to install an electronic zone valve for the living room and a room thermostat.

Ground floor joists touch the soil - is this a problem???

Arnold — Mon, 12 Jan 2009 17:15:01 +0000

hi Jack,

Although I have not read all your replies to this I would like to make a few points,

I had a similar experience terrace house front room, in my last terrace there was two to three ft of space under suspended floor 30yrs ago.

So in this house owned 12yrs I thought I would lift section of floor (chipboard) crawl under and insulate underneath with Lambs wool hung from netting between joist's..The snag was most of it was filled up like yours -- previous builders put rubbish in to save removing it from site.
I soon realized I would have to remove all the floor if I was going to do what I had intended. I decided to insulate the section I could get too which was by the window and seal the edge of floor to wall with mastic the end result was it was a lot warmer and if I need TOO. Next time insulate above the floor with a product similar to that advertised on page 71 of the GreenBuildingmagazine which is about new products.

If it was me I would lift some more of your floor around the edges to see what they are like especially as the floor boards do not appear to be physically joined together. Also do you have woodworm flight holes in the picture where you measured the joist. if so that is another cause for concern. Arnold

Ground floor joists touch the soil - is this a problem???

Davipon — Sat, 10 Jan 2009 19:37:13 +0000

You would need an awfull lot of concrete to 'just fill hole' best check with one of the architec bods on here about feasability.
I personally would put in a new suspended floor,cheeper,easier & probably a greener option,especially if you recycle some treated timber.

Ground floor joists touch the soil - is this a problem???

ali.gill — Sat, 10 Jan 2009 12:55:54 +0000

Small point but worth knowing is that floorboards like that sell in architectural salvage for around £1 a linear foot. So your existing floor is worth a few quid - do not use it to feed a bonfire.
Plenty of these floors have been replaced with a concrete slab.
If the property is that old then it is highly likely that there is very little in the way of a foundations so penetrative investigation is a definite.
If the property is semi-detached or terrace then you may need to consider the party wall act depending on your chosen solution (i.e concrete slab), especially if the properties are stepped laterally parallel to the street.
Are there any extensions/original ground floors/external pathways that have been constructed with concrete ? if so these will prevent internal ventilation and externally will prevent drainage (moisture ingress at path/wall junction)
Heat losses will be at the perimeter walls as the floor is clearly not vented, the floor is dry as most of the subfloor is infill and your main issue is the area below ext. grnd level which i guess is where the rotting timber is located > in which case excavate externally and replace with stone chippings (you could also divert any surface water run off, further up the garden, away from the house - especially if garden/ground level is sloped as you suggest).

Insulation solution > excavate 50mm2 channel around internal wall perimeter and place 125x50 pir at the perimeter walls (drastically reduces cost and quantity of materials > embodied energy). Then spend the time and money you've saved fitting draughtstrips and loft insulation.
Thinking laterally your floorboards are on top of bearers that are on top of thermal mass.

Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Fri, 09 Jan 2009 20:31:50 +0000

Many thanks for all the advice.

Sounds like I need to dig an exploratory hole to find out how deep my foundations are.

Posted By: James Norton
Another really big factor if your doing it yourself is which you fancy doing!

Yes! Well, to be honest, if I do rebuild my ground floor then this will be the largest DIY job I've ever attempted (although I do think it's just about within my ability as long as I do lots of research and give myself plenty of time to do the job). I've built decking with concrete foundations and that sort of thing but I've never done quite such major surgery to an existing building!

Posted By: DaviponJoist hangers aren't usually a feasable solution in older houses as the bricks are usually a soft composition & tend to crumble under loading.

Oh, bother. Thanks for the advice.

This forum really has been a life saver. I dread to think what would have happened if I'd attempted the job without asking here first!

Ground floor joists touch the soil - is this a problem???

James Norton — Fri, 09 Jan 2009 17:58:02 +0000

The dirt under the floor is 70mm below the floor level so to provide enough space for joists and ventilation you would need to excavate more like 330mm...(ie ground under floor 400mm below the underside of the floorboards. If the bottom of this hole is below the level of the foundations then you have just undermined the foundations and need to under pin. If not and if you can get the ventilation then no worries go for the suspended timber option.

Another really big factor if your doing it yourself is which you fancy doing!

Got to go and cook tea

J

Ground floor joists touch the soil - is this a problem???

Davipon — Fri, 09 Jan 2009 17:08:16 +0000

Joist hangers aren't usually a feasable solution in older houses as the bricks are usually a soft composition & tend to crumble under loading.If you dig about under the soil you may find that it's loose debris on top of a lean mix oversite (concrete base)This can act as a surface to prop good joists from while you renew timber on bearing points,it might be easier(figuratively speaking)to put in extra strip footings & bearing points than faff about with deeper joists,cheaper timber costs too.Apologies for misspelling on mortar!

Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Fri, 09 Jan 2009 15:16:52 +0000

Good point.

The house is built on a slope but the ground floor of the house is on a single horizontal plane. So the floor level at the front of the house is probably about 2m above ground level but the floor level towards the back of the house is quite possibly slightly under ground level.

So do you think it's possible that I could disturb our foundations if I dig the floor out by 15cm? Is a solid cement floor a better option? I suppose it's impossible to tell without seeing the building up close and personal.

Ground floor joists touch the soil - is this a problem???

James Norton — Fri, 09 Jan 2009 15:05:05 +0000

Where is FGL in relation to FFL ? if the floor level is well above ground level then there is less of an undermining issue, if not it might prove a difficult void to ventilate and you'll need to investigate the foundations... engineers.... big hole in you living room for ages... etc. Are you sure suspended timber is the best option in this case...

J

Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Fri, 09 Jan 2009 12:21:03 +0000

Great picture! Yikes, that must have been a lot of work! (By the way, how did you manage to embed a photo into your post?)

My problem is that who ever built my ground floor couldn't be bothered to build proper suspended timber floors; instead they just laid the joists directly on top of the soil! The existing joists are too thin to cope with the span without being supported by the soil.

http://xlk.org.uk/ext_images/house/DSC_0079.jpg

So I have to remove the joists and dig down anyway... so hopefully I can use whatever sized joists I want (I assume using larger joists just means that I have to dig further and use the correct metal supports) and I'll use metal supports to hold the ends of the joists (if that's acceptable?)

Ground floor joists touch the soil - is this a problem???

Davipon — Fri, 09 Jan 2009 12:06:04 +0000

dan_aka_jack hopefully here's a picture of dwarf walling for your info.

My joists were in as bad a state as yours so I replaced all ground floor.Your existing spans should be ok if not changed from original.Any deeper timber for joisting will mean a higher floor level or lower bearing,so bottom of joist deeper in ground.
You ideally need a clear space below joists for air movement & to stop moisture transfer.Joist should sit on timber plate on mortor bed on dpm on mortor on brick work.

Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Fri, 09 Jan 2009 11:29:12 +0000

Many thanks for all the help - your advice has all been extremely useful, thank you so much.

Richy, thanks for the joist span document. That's good news... it sounds like I wont have to fabricate any extra sleeper walls if I get wood thick and deep enough to cope with a 4.5m span. The living room is currently about 7 meters long but the room definitely used to be 2 rooms and I'm 99% certain that the dividing wall was constructed from a single layer of bricks. I assume that the brickwork which used to support the dividing wall still exists under the floor boards and I could use this as my sleeper wall. I will pull up some more floor boards this weekend to explore what's down there.

Tony: there certainly are air vents in the external wall entering what I assume is the under-floor space. But given that the joists touch the ground, I doubt the underfloor space is ventilated especially effectively. Many thanks for the info about woodworm not eating dry wood; I didn't know that so I was a bit baffled about why the joist was rotting AND the floor board showed evidence of woodworm. But now it's much clearer!

Ground floor joists touch the soil - is this a problem???

tony — Thu, 08 Jan 2009 23:11:31 +0000

Re edge joist -- looks like little dampness as woodworm won't eat dry wood. Reduce g/l outside, check gutters etc.

Is the floor ventilated from outside?

Ground floor joists touch the soil - is this a problem???

richy — Thu, 08 Jan 2009 21:51:49 +0000

The building regulations dictate joist sizes/spans, look here: http://www.haringey.gov.uk/trada_span_tables.pdf

Ground floor joists touch the soil - is this a problem???

dan_aka_jack — Thu, 08 Jan 2009 16:49:13 +0000

Great, thanks for the reply.

By the way, here's a photo of the end joist (nearest to the external wall) which isn't a happy joist:

http://xlk.org.uk/ext_images/house/DSC_0003.jpg