Suspended Timber floor over earth - internal vents?

[Anja]

Hi,
Newbie here wrestling a 1760s house into a cosier home. Very grateful for wisdom offered.
Most of the house has agricultural strength (!) concrete floors and, in places, slathered over very soft red bricks walls too.

However one front room about 4m x 4m has suspended timber floor on sleeper walls over earth with 3 air bricks vents to the outside. Probable that the sleeper walls (painted with bitumen) were added along with new joists and floorboards sometime mid-C20th - about 300mm above earth.
There is some rot in joists adjacent to the walls where internal concrete patching render and gypsum inhibit airflow & breathability. Air bricks now free from debris and clear to external.

Remedies??

• Free up any sleeper walls that have earth debris above bitumen layer
• Chop out rotten joists and replace or sister where conditions suggest
• Gypsum to be removed at low levels from walls
• Look into insulating

There's a further piece to the puzzle - alongside the opposite internal wall there are 4 vents cut through the floorboards ( had plastic grilles which look like the work of previous owner with limited understanding of old buildings.Are these necessary to the cross-flow of air to make our suspended floor more effective again? I just don't know if they help or hinder.
Thank you from me & the toad we found under the floor!

 

[Cubist]

Air-bricks were not introduced in the UK until the late Victorian period and so these were probably a later addition to the house. A single wooden floor at ground level was not uncommon and would usually be kept as a room for the entertainment of guests and visitors. I would be speculating but it may be that the original wooden floor may have been seriously damaged due to ineffective ventilation and was replaced at some time in the houses history. The plastic vent coverings may have been added much later in the houses life to improve air-flow. Is there ar fireplace in that room?

 

[Anja]

Yes - agreed - much later floor added with air bricks. The sleeper walls have cementicious mortar and a bitumen course under the joists - I think this is usual mid C20th Century practice?
There's a large fireplace - big chimney partially capped at top so some air circulation I guess.

 

[Cubist]

The fire would have helped to pull air through the under-floor void thus driving the essential airflow which would otherwise have been poor with air-bricks in just one wall. Bitumen as a doc dates back to the Edwardian period so early 20th onward.

 

[Anja]

The fire would have helped to pull air through the under-floor void thus driving the essential airflow which would otherwise have been poor with air-bricks in just one wall. Bitumen as a doc dates back to the Edwardian period so early 20th onward.

Thank you - that all rings true.
Anything further we need to do to maximise the efficiency of the floor?
Do you think the floorboard vents help?
Cheers

 

[Anja]

We also found what appears to be an asbestos pipe running from under the hearth and seems to share the external air brick/vent but doesn’t effect air to the floor. From a previous back-burner perhaps? It is all in tact & will stay put!

 

[Cubist]

Anything further we need to do to maximise the efficiency of the floor?
Do you think the floorboard vents help?

I can't think of anything else other than perhaps insulation but others here know more about that than I do. However, the vents will be of help even if you have no heating in that particular room. The ambient temperature of the house should generate some airflow under the floor to inhibit/prevent wood rot.

what appears to be an asbestos pipe running from under the hearth

Intriguing. Any more data concerning that pipe. e.g diameter, nature of any fittings?

 

[Anja]

Great thanks.
Definitely will look into insulation soon.
The pipe is about 150mm externally.
All very much intact. We intend to leave it well alone.

 

[Cubist]

Good idea, but wrap a warning label around it for the future owner that comes across it.

 

[Anja]

Brilliant idea - will do

 

[Flyfisher]

Is the pipe still being used for anything?

It looks like 'cementitious asbestos', ie asbestos fibres embedded into the cement construction of the pipe. Similar to asbestos-containing corrugated roofing sheets often found on old garages and other outbuildings. There's no need to panic as the asbestos content is firmly trapped within the cement matrix and as long as it's not disturbed it is quite safe. Even if you wish to disturb it, eg remove completely, it is fairly safe to drill and cut as long as the material is wetted with water to prevent any dust escaping. This relatively low risk is why such things do not require an asbestos handling licence, unlike the long-banned asbestos-containing fibrous pipe and boiler lagging materials, and also why the material can be disposed of at council refuse centres as long as it is double-bagged and labelled.

Lots of information on the HSE website, eg: https://www.hse.gov.uk/asbestos/licensing/non-licensed-work.htm

 

[Anja]

Thank you - we suspected as much.
It’s in an awkward place - & the end of it seems well concreted in deep under the many layers of hearth. Happy to leave it in situ. Fishing it out I think would be quite a feat and invasive if it’s not doing any harm in-tact.
I’ve labelled the adjacent joists so future ‘finders’ knows where it travels.
Still not certain what it may have been for, I saw another post with something similar suggesting old back boiler or Baxi. This makes sense??
Thanks for your advice - very much appreciated