underfloor ventilation question. i'm new, pls be gentle ;-)

[vonatt]

hi all. newby virgin here.

i've been having a mooch around these message boards and have found lots of useful info, but wondered if there's anyone out there who can give advice for my particular question. there's several parts to it really so i'll try and break it down.

long story short, i was selling up, but now i'm staying... the timber living room floor and joists were replaced as the lot was rotten and riddled with woodworm, then the same people laid laminate floor over the top. i don't like it, it's cold and noisy. the laminate is therefore going! whilst i do this i want to be sure that insulation and ventilation is sorted.

i'm unsure as to the best solution... is it better to go to the expense and disruption of getting the floorboards up and insulating between the joists, or would an insulating layer above the floorboards be feasable?

the next thing is the ventilation under the floor. the room runs full length of the house, and there are airbricks front and back. when i bought the house 15yrs ago, surveyor's report recommended bigger airbricks on the front. this would be pretty simple, but can't see how it will improve airflow really as there is a 'kind of' conservatory on the back of the house which presumably just blocks the airflow. (i say 'kind of' conservatory... it's more of a lean-to, stifling in summer, freezing in winter). the airbricks on the back of the house are slightly below the (concrete) floor level of the lean-to, with a sloping channel down to them.

is there anybody in the know can advise me on what to do
i'll have a bash a most diy stuff, but want to make sure i am doing the right thing.

many thanks in anticipation

 

[vonatt]

ok, slight update.

i'd assumed putting bigger/extra airbricks in would be simple enough, but having actually looked i don't think it's possible. the bricks there at the mo are the clay type and look to be 9x6in. directly below there's the thick line of mortar (dpc of some sort?) and the course above has obviously been injected at some point as there's that attractive 'two blobs' on each brick.

i'm seriously concerned about inadequate ventilation under the floor, given the state of the old one that came out... i *know* this is a problem

pleeeeease is there anyone that has advice?

 

[RedHerring2]

Hello, I'm only a DIY'er but I'll offer my opinion whilst I think the more experienced people on here might be out making the most of the reasonable weather.

First of all; I suspect, as you probably do also, that underfloor ventilation should vent to outside. Any venting into another building is likely to a) negate any differential in air pressure so that much less ventilation actually occurs, and b) any ventilation may well be warm, moisture laden air from the "conservatory". I suspect that current reg's insist on venting to outside but no doubt your conservatory pre-dates existing reg's.
(Edit: Just remembered conservatories are not subject to Building Regulations, depending on conditions.)
Depending on the width of your conservatory that might be preferable to the other option of making your internal floor a solid floor, requiring no ventilation. (Unless it's semi-detached or detached and you can create new vents in the side wall(s).)

Having investigated the situation for my own project, I have seen somewhere, but forget where, that 2 X 100mm underground waste pipes are used to bridge the concrete floor under the conservatory. That's two pipes for each 9" X 6" vent.

I'm not sure that the various DPCs are relevant, given the info' you've provided so far.

Secondly; I would think that lifting the existing timber floor and placing insulation underneath is more cost-effective than insulation on top, then another floor on top of that.
And while you're at it, clear out any building rubble left under the floor. It's not unknown for builders to use that place as a tip.

 

[vonatt]

thanks for your reply redherring2 much appreciated.

my preference would be to have a solid floor installed but at this point in time that's not an expense i can afford. recently had to have the solid floor of the other half of the house (just over half actually) done, and it cost four and a half grand!!! that included taking the old one out and disposing of it though. (and that was the cheapest quote... i had quotes of nearly double that!)

regarding ventilation under the boards, i'm at a complete loss as to what to do to get some airflow going on to protect the new joists and boards from condensation/damp or whatever... i don't relish the idea of smashing up the 'conservatory' floor, laying channels, then re-laying floor... also, channels would need to slope down and away slightly, and the floor levels just won't accommodate this. i'm stuck

 

[JohnD]

do you live in a teraced house with no side walls? Does the conservatory completely cover all of the back wall? Do you have any chimneys?

 

[RedHerring2]

Forced ventilation, if it is feasable?

But I have no idea how much, how often or for how long.

I suspect it needs to be flowing from the outside into your conservatory.

Or leave the conservatory windows permanently open.

 

[vonatt]

rh2 i know nothing about forced ventilation, will have to look it up.

johnd, i live in a semi, but the timber floor is sandwiched between the party wall and the solid construction floor on the ground floor of the other side of the house, also the conservatroy does run accross the full width.

 

[JohnD]

any chimneys?

I bet you wish you had thought of this before the solid floor was laid

does the conservatory have brick side walls?

 

[RedHerring2]

Perhaps I should have said mechanical ventilation, i.e fan assisted.

 

[vonatt]

sorry, forgot to say... yes there's a chimney breast, which accommodates the back boiler for the central heating (plus fire on front).

the house was being sold so the timber floor was replaced a couple of years ago as i knew it needed doing (and boy oh boy it was baaaaaad). the solid floor was ONLY done as the buyer's surveyor called for a sulphate test... this showed a 'medium risk' and no damp proof membrane present, and the mortgage company insisted the lot be ripped out to a certain depth and redone (this entailed removal of the kitchen, downstairs loo etc... then putting it all back in again after... nightmare!). anyway, it's done and i have a nice shiny completion certificate to prove it's all up to scratch... then the buyer dropped out sold it agian, but due to personal circs, i dropped out and am now staying put. had i known i was staying, i'd have done things differently... ain't hindsight wonderful

anyhoo... so that's my life story

 

[JohnD]

oh, just the one chimney, and that is in use? pity, as a chimney can be vented from underfloor, if not in use,

 

[RedHerring2]

But could it be put to use? By having a floor mounted vent to feed air to the fire, thus drawing air from under the floor?

 

[JohnD]

you could do. In some expensively-built stately homes, you find a brass grille in the floor in front of the fireplaces, to provide air to the fire without causing draughts in the room.

the other approach would be to put a duct in the conservatory going through the house wall at one end, and out to the garden at the other. If you put these very low, and tight to the side walls, they need not be very obtrusive.

the advantage of vents on two or more sides of the house is that you will get a throughflow whenever there is any breeze. Even a bay window, where the two sides point in different directions, will help, but you will still get an area of dead stagnant air at the conservatory end.

 

[vonatt]

appreciate your input guys... thanks.

still don't quite know the best way to tackle this :-/ there's just no straightforward way of doing it. (ie: one thing is going to lead to another).

i think the *best* (but not the easiest) solution will be to lower the level of the airbricks on the back (they're half above and half below the level of conservatory floor), bury some ducting (the floor is sh*t and needs re-doing at some point anyway... it's a botched diy effort by the previous owner and you get seasick walking on it as it's lifted and cracked all over the place. i doubt there's even hardcore under there, it's not affecting the house though so has been left to get on with it up to now). i'd then need to suss some sort of periscope effort to bring the ducting above ground level outside. consevatory walls are single width breeze block, and are ply lined inside, pebbledash render outside. there's also a lip/rim (don't know how else to describe it) of concrete all around the outside bottom edge, which is around 150mm high x 150mm deep. right in the blimmin way in other words!!

this is a bigger job than i'd hoped but can't really see what else to do. ducting above ground level would be easier, but only possible for one vent on one side and i just don't think that will be enough.

it might have to wait until spring now

 

[RedHerring2]

Check out these two similar threads:

//www.diynot.com/forums/viewtopic.php?t=245416

//www.diynot.com/forums/viewtopic.php?t=171482


Some good info' in there.