Mechanical Ventilation for Basement

[KerryFl]

We have just brought a Victorian terraced house, with 60sqm size basement (half crawl space). It has soil on floor and high humidity levels of 99%. It has some air bricks to the front but not at the back. Its about 160cm high so want to use it for storage.

I think mechanical ventilation best but anyone have experience or advice on units to use? We've also been advised to put a membrane on the floor with concrete screed on top. Any thoughts on this or alternatives? Many thanks.

 

[Cubist]

I believe there are others here who have relevant and direct knowledge and experience, but ahead of their input here's my two-penneth;

Whilst a concrete screed would provide you with a solid and level base for any belongings you want to store, the net effects would merely be, because of the DPM membrane, to push rising damp from the earth below toward the walls. As the walls too, at least those below external ground levels, will be exuding damp into the atmosphere of the basement the net gain in terms of damp reduction could be little to none. This may also mean that the surface of the screed may become wet, perhaps to the extent of puddling, and thus cause damage to your stored goods.

The extant air-bricks could provide an excellent route via which a PIV system can push damp laden air out of the basement, however, you may need to consider where the system needs to be sited to assure best effect and air-flow. I also have a suspicion, but can't confirm, that these systems may not perform as well as they might during periods of high humidity outdoors. Hopefully someone will be along to refute that and perhaps make a more positive recommendation.

 

[Flyfisher]

A period cellar (as opposed to a modern properly waterproofed one) is really just a hole in the ground and 99% humidity is pretty much all that can be expected given that the surrounding ground is an almost limitless source of moisture. Remove the moisture-laden air in the cellar and it will simply draw out more moisture from its surroundings in an attempt to restore the natural equilibrium.

I have a cellar and some years ago installed a dehumidifier, which did an excellent job at extracting so much water from the air that I soon got fed up with having to empty it every day or two. To solve that problem, I then installed a condensate pump, which collected the extracted water and when full would switch on a pump for a few seconds to pump the water up and out of the cellar. This arrangement worked extremely well and meant I didn't need to regularly check progress, which I left to a min/max humidity meter.

There was only one problem - it made very little difference to the humidity in the cellar!

That's not to say it's wasted space because we still store stuff down there, but only things that are not affected by high humidity. Wine is a good example but anything else in sealed bottles or cans are perfectly fine down there. I bought a plastic mesh shelf unit from a garden centre (the sort of thing for use in a greenhouse), which is pretty much immune to the humidity and keeps things off the floor as well as providing lots of storage surfaces. The other option, which I've not tried, is to buy some large air-tight plastic containers to keep the contents safe from the surrounding humidity. Good quality air-tight containers might not be cheap but I reckon they'd be a better investment than spending it on pouring a new concrete floor.

 

[stuart45]

Thinking outside the box a bit for a concrete floor, You could do away with the DPM, and use a concrete mix with a much higher gravel content.
This would allow any surface condensation to drain down and help prevent rising damp without pushing it up the walls. You do get a slightly rougher finish, but you would have a solid floor. This method is sometimes used for car parks, as it's really porous.

 

[Glenn586]

I'll be watching this thread closely as I've also been toying with having a trickle vent constantly running in the cellar. I still have hopes it will make a man cave one day.

 

[larry]

I do have an MVHR unit but not a basement. Given the various posts on here I can feel grateful for not having one!! I do have a recurring dream though that involves a flooded basement... Maybe I need to stop reading horror stories on here!!

I'm intrigued as to whether you'd plan/intend to use the MVHR to extract the damp air, or to supply fresh air.

I guess in the basement you aren't getting any heat that is worth recovering (like you would in a bathroom) which makes me wonder about benefits of extraction, so interested in hearing the thinking about how this would work....

 

[Flyfisher]

I'll be watching this thread closely as I've also been toying with having a trickle vent constantly running in the cellar. I still have hopes it will make a man cave one day.

A period cellar would make a perfect man-cave and would be just like a genuine, natural cave . . . . cold and damp

 

[Glenn586]

Sounds Perfect. The Mrs doesn't like cold and damp.

 

[thebadger7]

We have a cellar, with only a vent on one side via coal shute (extension at back of house so no air bricks that side)
Installed an extractor fan, and a floor fan, that runs on a timer for an hour or so each night. Idea being to get more of the air replaced.
Seems to be doing an OK job. Humidity is around 90% but doesn't smell musty down there.

 

[mh12]

We have a cellar, with only a vent on one side via coal shute (extension at back of house so no air bricks that side)
Installed an extractor fan, and a floor fan, that runs on a timer for an hour or so each night. Idea being to get more of the air replaced.
Seems to be doing an OK job. Humidity is around 90% but doesn't smell musty down there.

Thank you for sharing. Extractor fan is self explanatory but what is a floor fan?

My cellar is damp and gives off a musty feeling so need to follow suite.

What type/make of extractor fan did you opt for?

Thanks

 

[thebadger7]

I used a "Vacmaster Air Mover" floor fan. Idea is that this pushes air at floor level, and extractor removes air at ceiling level to create air flow.
I've just used a bog standard bathroom extractor fan for now to prove it works, I now should upgrade it to something better quality.

 

[KerryFl]

Thanks for your responses, much appreciated. I have enclosed a floor plan, as I don't know how to the airflow in the crawl spaces, as it is so limited. Any thoughts or ideas would be much appreciated.

 

[Glenn586]

View attachment 14980
Thanks for your responses, much appreciated. I have enclosed a floor plan, as I don't know how to the airflow in the crawl spaces, as it is so limited. Any thoughts or ideas would be much appreciated.

Tornado Silent dMEV Continuous Running Extractor Fan with Humidistat​

Assuming cellar is 2m high and crawl space is 0.7m you are looking at approx 80m3. This fan is programmable and capable of moving anywhere between 18m3 per hour and 126m3 per hour. (1w - 8w).

My cellar is half the size of yours and as a starting point I'm going to programme this fan to run at trickle so I'l be recycling the whole volume of air approximately every two hours. It also has an in built humidistat that you can programme anywhere between 40% and 90%.

I'm venting out of the bricked up coal shoot. The air from our warmer drier first floor will be finding it's way into the cellar under two cellar doors.

I'll be installing in the next few weeks and am hoping to see a difference around a month after. I'll keep this thread updated.

​

 

[KerryFl]

It would be great to hear how you get on, Glenn586. My experience with general extractor fans with humidistats, is that they aren't that effective on their own. Would be really interested to hear how yours works out, so please do post back on here. Thanks.

 

[Glenn586]

The fan mentioned above is installed. I set it to run continuously at 3w which is a penny and a half a day, it's only just audible when you enter the cellar. You will see that the oak beam above it has quite a lot of decay from woodworm. It's still wet on the left hand side from where I sprayed it two months ago. I've marked this with a red felt tip pen so I will be able to see any acceleration in drying. I'll keep updating this thread for reference.

 

[KerryFl]

The fan mentioned above is installed. I set it to run continuously at 3w which is a penny and a half a day, it's only just audible when you enter the cellar. You will see that the oak beam above it has quite a lot of decay from woodworm. It's still wet on the left hand side from where I sprayed it two months ago. I've marked this with a red felt tip pen so I will be able to see any acceleration in drying. I'll keep updating this thread for reference.

View attachment 15085

That's brilliant, Glenn586. Yes, please do update us on here, it will be really interesting to see what happens. Are you doing only extraction or have you got a fan or something to add airflow too?

 

[Cubist]

It's still wet on the left hand side from where I sprayed it two months ago.

I'm a little surprised by how long it's taking to dry. What did you spray the timbers with?

 

[Glenn586]

I'm a little surprised by how long it's taking to dry. What did you spray the timbers with?

Lignum woodworm killer diluted with water. It had fortnightly applications until I realised that it won't work until you can get the wood dry so it was bit like peeing into the wind.

 

[Glenn586]

That's brilliant, Glenn586. Yes, please do update us on here, it will be really interesting to see what happens. Are you doing only extraction or have you got a fan or something to add airflow too?

I'm going to see how this single Fan works out. From what I gleaned by reading up on the matter, an identical Fan blowing air into the cellar from my ground floor would create positive air pressure which would be even better. If I do go for the extra fan blowing into the cellar I'm hiding it in this under stairs dog kibble cupboard. As you can see the door is very leaky at the bottom right hand corner so I reckon airflow won't be restricted.

 

[Cubist]

Lignum woodworm killer diluted with water. It had fortnightly applications until I realised that it won't work until you can get the wood dry so it was bit like peeing into the wind.

Oops, and limited air movement in that space won't be helping either.

BTW - I rather like the 'salvaged timber look' on those stairs.