Help with sub floor ventalation

[mobucl]

Hi, this is my first post and im not a DIY expert so please be gentle!
Last year i bought a terrace house in the Netherlands which was built in 1910 which has a sub floor. The problem is that it has a single storey extension on the back with a concrete base and there is no air vents at the back.

Clearly this is a big problem as the chipboard-like floor material (which was obviously installed last time the floor was repaired) has rotted through at the front of the house. On investigation I found all of the joists and boards were very wet, so now im using normal house fans in the hole where the rotten floor was to dry it out.

I think the best way to fix this is to run a pipe from the edge of the old floor where it meets the concrete up through the room and through the single storey celling thus allowing through flow. Having never done this however i need some help!

1. what diameter tube should i use (it needs to be about 3 meters long)
2. With this arrangement should i also install some type of inline fan (ive seen a few on the internet) connected to a moisture sensor under the floor? If so can someone recommend a good (but relatively cheap!) and mainly quite one.
3.If i dont need a fan do i need to have some sort of shut off valve to avoid 'whistling' noises in the tube when it is very windy.
4. As the pipe will be vertical outside what should i use to cap it off to avoid rain but allow airflow no matter the wind direction?

Sorry for the long message but i hope it is detailed enough and someone could provide me with some answers.

Thanks!

 

[^woody^]

Are there vents at the front of the house? You really need cross ventilation so that air moves across all of the floor void from front to back

Use of any fan is unorthodox, but your idea may work. However if humidity is always high then the fan will always be on and must be rated for such use

You may want to investigate a " positive pressure " fan system where by the low RPM fan unit is in your property and this is ducted below the timber floor and it pushes air in the void out through several vents. Again this will be unorthodox and may not be viable

In any case any mechanical fan could cause draughts to your room via any gaps in the floor boards, so consider this

 

[mobucl]

Hi ^woody^,

Thanks for your reply. Yes there are vents at the front of the house. There are two newish pipe vents (~ 5 - 8 cm diameter) and a very old air brick which may or may not be blocked ( i need to check this and exact measurments but cant do that untill time at the weekend!).

My idea was then the there would be air flow from the front of the house to one back corner of the original house (as i really only want to put in a single vent at the back to avoid an ugly box either side of the open plan living room and kitchen). This is a distance of ~ 12m

This back vent will then be a pipe (drain pipe like??) in a hole through the floor and to the single storey roof. The only reason i suggested an inline fan was i am not sure if the air flow would be sufficient with this setup as it needs to travel 'up' the vent at the rear of the old house.

Do you think this might work without a fan? I suppose i can go with the cheaper no fan option initially and monitor the humidity and then add a fan unit later if needed......

Thanks

Matt

 

[stuart45]

Fans are popular in certain U.S.A. states which are really hot and humid in the summer, and floor timbers can have high moisture contents.
However in the UK which has a similar climate to Holland they are not common.

 

[mobucl]

So i think i will try and go without a fan at least at first.

But can anyone give me an idea about the diameter of the tube to the roof ( i was thinking i could just use a drain pipe?)

Also what should i cap this pipe with to avoid rain entering but allow good air flow.

Finally where it comes through the roof this area will need to be resealed (the roof is a bitumen sheet type flat roof i think) I will get a professional to do this but will i need some form of metal sleeve to protect the plastic tube?

Thanks

Matt