Underfloor Fans

I have an Victorian style house built in in the 1900's. Unfortunately being an older house, i do tend to get moisture problems and the only way the house gets a breeze is through these tiny 10cm x 20cm floor vents (everything is blocked up, not like other homes on stumps where a breeze can run freely across).

I've installed underfloor vent fans Quad Fans - Envirofan Sub-Floor Ventilation Solutions, Sydney - Reduce Mould - Prevent Termites several years ago and that hasn't done much, the ground is still constantly damp.

I'm thinking of going out to bunnings and buying the following Dynabreeze 30cm Yellow Extraction Fan with a hose Dynabreeze 5m Extraction Fan Hose.

Very much aware that these things aren't going to be quiet, however I only intend to run this every so often (while I am out at work etc).

I'm either going to:
1. Put the entire thing under floor and run it for several hours at a time (I'll use a timer or something to give it a break)
2. Connect it to the house and feed that under the house. The fan itself will then remain above the floor.

Is there anything i can potential break? Surely during up the ground is better than having it damp. Thoughts?

 

Injection of silicon into brickwork to create a damp proof course wherever you have rising damp.

Improve subfloor ventilation by replacing the vents with larger wire vents.

 

This is the hard part... i can't. Don't have the room.

The previous owner cemented around the house, as a result the some of the vents are actually on the same ground level as the cement driveway. I can't go higher either due to the height of the existing floor. The vents are already wire vents.

On the side where i do have the height, I already have 3 ventilation fans installed that suck air out of the subfloor and out.

 

Are the fans really extracting, or maybe they do next to nothing unless all the floor etc is sealed up as well.

Just a thought, I lived in a place that was like this, it was a mouldy old hole, the problem really laid in the land itself, the location, the surrounds and that basically it had about 6-12 inches of dirt on top of rock, so rock acted like a pool and dirt retained moisture.

 

Revisiting this thread after a year.
Haven't done anything, so the problem is still there.
I want to make sure the kids don't have health problems in the future due to poor ventilation.

Your comment makes a lot of sense, its extracting air.... but from where? There are cracks everywhere, so its probably quite ineffective at its job.

I've also looked at those subfloor "specialists" and looked at their "solutions" which involve ducting that "extracts moisture" and moves it out. I can't see how that is really effective anyway.



I'm now thinking of getting Expol subfloor insulation done - my theory is that this will block the cold air coming up and create a better seal so that air can actually get extracted out.

Then coupling this with 1 of these fans per bedroom (placed next to the vent)
Ezi Air Inline Axial Booster Fan - 10 to push air around and out towards the current Enivronfan extraction fans.

Aim is to create the draft that would flow naturally on better ventilated houses.

Thoughts?

 

neK,

Google: positive pressure ventilation systems
Ones like Ventis force air out of the house.
It's hard to get your sub-floor area dry in the recent rains Sydney experienced for 3 weeks on end especially with your setup currently.
Cheers,
Alan

 

@Propertunity - The subfloor in my house hasn't dried up since i bought it 7 years ago.
Damn thing has always been a bit moist. There's bugger airflow underneath, and the extraction fans do a bit, but not a lot. Hence why i want to get fans just to blow air around in the subfloor so it makes it way to the extraction point.

That said, how does that positive ventilation system work?
It sucks air in from the outside, filters the air and pushes it out into the room.
In theory, that would create the positive pressure, but then where does the excess air pressure go?

That site (like many others, don't really explain it).

Expelling heat and humidity where?

So they are saying don't open the windows.... so where does that dirty heat and humidity go?

Also, have you used (or know people who have used it) before ?

 

Is this a drainage issue?
Do you have a cracked or broken water pipe under the house?
Is rainwater diverted away from the foundations?
Marg

 

Should have used a BA for the purchase

Positive air pressure inside forces air outside thru leaky windows, doors and floor boards etc so damp can't enter the house.

 

I don't think its a drainage issue.
I think its simply due to the levels of the house.
Its not wet, just not dry. No large areas of wet, just consistent not quite dry areas.
House smells musty if no windows are open.

I've drawn a cross section of my house.
Unfortunately the previous owner decided to concrete the side of the house, but instead of ripping out the old concrete, he concreted on top.

As a result, the side air vents are the same level as the concrete, which i don't believe helps the cause.

That said, it probably don't get much air flowing through

 

Yes that does make sense.
Which means putting some subfloor insulation would actually be a bad thing if i used Positive Air Pressure.
Any idea how much these systems cost - as a ball park?

 

Can you have the concrete removed and relaid to a better level?
Enlarge and/or increase air vents?

Treat the cause of the problem rather than try to deal with the consequences?
Marg

 

I believe the gap between the top of the vent and the floor is 5cm at best.

As for the concrete removed, its a very large area that would need to be redone. About 2.4m x 20m for the side section. I would then need to redo the front (at least $3k for me and $3k for the neighbour as we share the driveway) otherwise when it rains all the water will pool up on the side section and make the situation worse.

If i did redo the concrete, it would end up costing close to $20k.

 

Ouch!!
Marg

 

I would like to respond to Nek's (underfloor fabs) post about installing the Envirofan Quad fan systems. Firstly Envirofan is not mean't to dry the ground but to provide the removal of humid air from the sub floor area. As wet weather is perpetuating the Envirofans will dry the ground to some extent until the next downpour however bear in mind that ambient moisture content in the ground is not an undesirable thing as it stabilizes the ground and this is true in reactive clay soils. So damp soil is not a bad thing, our objective is to remove the humidity which left unchecked will penetrate into the habitable area and affect timber structures. At 5.5m3/min the Envirofan Quad Fan system will do this. For a dwelling more than unit may be needed. Envirofan sub floor ventilation is not based on m2 but on 4 air changes per hour. This is done by estimating the volume m3 & dividing it by the airflow rate of the Envirofan which is in m3/min and the goal that should be reached is 15. Anything higher than this figure needs another Envirofan to be incorporated which will bring this figure down. Another factor that needs consideration is the shape of the building and construction type (eg solid brick, brick veneer)The time clock function we set from 8am-5pm as this will allow dry air to be drawn into the sub floor during daylight hours & switch off at night when the air is moist (especially during winter)

 

@enviro-fan Thanks for clarifying that. Unfortunately that wasn't what I was told when I first inquired about it several years ago... I was told that "the ground will be dry within a few months".... 7 years later, it's still moist.

That said, your response about changing air does make sense. I currently 3x Enviro-fans set to extract air. I do not have any Enviro-fans sucking any air in, nor do I have any ducts. This was part of the reason I wanted to invest in some more fans to blow any stale air towards the Enviro-fans. What are your thoughts on this? Do you have any suggestions on how I can maximise the air flow underneath my house?

On another note, I've just bought 78.3sqm of Greenstuf Subfloor Polyester insulation (Cost me $350 or so), so I'm going to crawl under the house and give this a shot - still reckon I need fans though to push air around.

 

What we have found beneficial with a job that was done in Picton (NSW) many years ago which we followed up about 12 weeks later on was a Envirofan set on induction (inducing the air or positive pressure) into the sub floor which was on the sunny aspect of the home (facing west) and I believe it was about summer time (there were no extraction systems) installed and in the 3m2 space, according to the client there was a significant drying effect on the sandstone. So we adopt the principle utilise induction Envirofans on the sunny aspect (north and west) utilising solar power as this will detect a nice sunny day and activate the fan impellers and draw in the dry air. When it is raining they don't activate. Use extraction (negative pressure) on the east and south where possible, achieving cross-flow ventilation which is the objective. Getting back to drying the ground if we return to El-nino would bet that the ground will start to dry superficially whilst retaining moisture lower down in the soil which in my previous post in not a bad thing, just don't want it to be in the sub-floor space or in the habitable area.

 

even though the concrete is up against the house you could cut sections out down to the sub floor level and cover with mesh to prevent rodents etc and may need a protection of some kind to prevent water entering.

 

Is there access in the sub floor, to install a fan to attach to a pipe? If there is you can use a snorkel 100mm pvc as it will stop the water getting in (if it not in a visable area as they don't look the best) similar to the Toyota Landcruiser. Could put a potplant in front or nearby.

 

Good idea

If they have poured over an old slab it's likely only max 150mm thick for a driveway. The top layer should pop off once saw cut.

Pvc can be painted or covered easy enough