underventilated suspended ground floor - can using superquilt (or similar) be a solution?

[swimmydeepo]

I did insulated a suspended ground floor in the past with very poor results= - the crawled space was under ventilated and the rockwool blanket installe= d between the joists used to get soggy under certain circumstances...as a r= esult some fungi started growing on the joists' surface - I decided to conv= ert the floor into a concrete one (the other half of the house had a concre= te floor anyway).

I've just stumbled across this product:=20

the graphics I'm led to believe that this design should provide a valid = alternative to cure problems due to under-ventilated sub floors (like the p= roblem mentioned above)....am I right?

Any feedback appreciated...=20 If so, would this product provide an even cheaper alternative?:

[Onetap]

alternative to cure problems due to under-ventilated sub floors (like the problem mentioned above)....am I right?

I don't think they say it's an alternative to adequate ventilation. The ventilation is to dissipate moisture coming from the ground through the oversite concrete.

[swimmydeepo]

well, the product is sold for another function: insulation...still, in my c= ase it would had been a more elegant and less costly solution than converti= ng the suspended under ventilated floor into a concrete one. I wish I'd see= n that graph years ago (the superquilt "crawl space" design) - there are ot= her applications but the one which involves stitching the quilt just under = the joist is just perfect.

That superquilt would solve 2 problems at once...you get insulation and dry= joists - worth every penny if considering how easy is it to install the st= uff.

I've used some SILVER FOIL BUBBLE WRAP INSULATION in the past but for a com= pletely different project - happy with this sort of product so far though I= don't think they provide much insulation.

[Tim+]

Or ventilate the underfloor space?

Tim

[swimmydeepo]

isn't that easy in terraces houses - ideally you want two opposite walls wh= ere to open small gaps in the wall to provide enough ventilation - I did tr= y with 2 ajacent walls but it didn't work...the bricks were also affected b= y some rot (maybe dry rot) and I took no chance.=20 By isolating the joist from the moisture coming from the ground (there was = no concrete) and also from a dodgy wall (as I said maybe infected by some f= orm of rot) one is guarantee the joist are kept healthy...the parallel of t= his form of insulation must be the warm roof (as opposed to the cold roof s= ystems).

[harry]

ts - the crawled space was under ventilated and the rockwool blanket instal= led between the joists used to get soggy under certain circumstances...as a= result some fungi started growing on the joists' surface - I decided to co= nvert the floor into a concrete one (the other half of the house had a conc= rete floor anyway).

d alternative to cure problems due to under-ventilated sub floors (like the= problem mentioned above)....am I right?

It's quite difficult to fix stuff like this properly especially if the space is restricted. The hardest bit is sealing the perimeter. The way they've shown doesn't seem practical.

[harry]

ts - the crawled space was under ventilated and the rockwool blanket instal= led between the joists used to get soggy under certain circumstances...as a= result some fungi started growing on the joists' surface - I decided to co= nvert the floor into a concrete one (the other half of the house had a conc= rete floor anyway).

d alternative to cure problems due to under-ventilated sub floors (like the= problem mentioned above)....am I right?

it. May even make it worse.

[swimmydeepo]

ults - the crawled space was under ventilated and the rockwool blanket inst= alled between the joists used to get soggy under certain circumstances...as= a result some fungi started growing on the joists' surface - I decided to = convert the floor into a concrete one (the other half of the house had a co= ncrete floor anyway).

lid alternative to cure problems due to under-ventilated sub floors (like t= he problem mentioned above)....am I right?

I agree with you about the U value declared...I don't believe any material = of that thickness can offer such insulation - in fact I'm considering using= a similar cheaper product (single foil bubble wrap) just to keep the moist= ure from the ground away from the joists and radiate the heat from the room= above - after all, this is what this type of product is good at, and floor= insulation works mostly on radiating heat (celotex and similar would be mo= stly wasted in this instance).

[swimmydeepo]

ults - the crawled space was under ventilated and the rockwool blanket inst= alled between the joists used to get soggy under certain circumstances...as= a result some fungi started growing on the joists' surface - I decided to = convert the floor into a concrete one (the other half of the house had a co= ncrete floor anyway).

lid alternative to cure problems due to under-ventilated sub floors (like t= he problem mentioned above)....am I right?

keep the moisture away from the joist then you don't need to ventilate...

[meow2222]

product:

> > > By the graphics I'm led to believe that this design should provide a valid alternative to cure problems due to under-ventilated sub floors (like the problem mentioned above)....am I right?

You're not going to get anywhere near a perfect seal in practice, so you've then got the same level of damp plus even less ventilation.

Multifoils also don't insulate as advertised at room temp, the figures are more applicable to radiant heat loss, which isn't the issue in houses.

NT

[swimmydeepo]

ve then got the same level of damp plus even less ventilation.

e more applicable to radiant heat loss, which isn't the issue in houses.

I have to disagree with you on some points here:

1) radiant heat is very relevant for floor insulation tough some marketing = propaganda try to push certain products which aren't that suited for the ta= sk and are at most an overkill - I might find some interesting links on the= subject but feel free to do your own search on that... 2) a perfect seal isn't required as the temperature of the joist's area is = similar to the one on the room above - the dew point became less of an issu= e =3D less risk of condensation...by the way, the design states that the fo= il sections should be stapled and overlapped but not sealed under the joist= - this allows any residual moisture to drip down safely (so it implies tha= t a complete seal isn't required nor desirable).

but I agree with you on the performance of multifoils - it's grossly overra= ted so I rather spend less (aluminum bubblewrap stuff) and make the most of= the radiant heat properties of aluminum...(basic science really - I trust = that).

The more research I do the more I'm convinced this is a very effective way = to solve the problem of under ventilated suspended floor - still, a real li= fe example would put any residual doubts to rest...is there anyone out ther= e who can provide some valid examples? (no just theory).

[The Natural Philosopher]

product:

>> By the graphics I'm led to believe that this design should

I had a long argument with a friend about this.

I reckoned with adequate ventilation you should treat it as a colad roof

- i.e. lift the floor, stick celotex between joists, foil tape over and re-lay floor.

He reckoned the better place for the vapour barrier was actually under the joists allowing any moisture to be driven upwards into the room . I didn't like that as the vapour barrier itself could get very cold and condensation would happen on the inside of it.

[swimmydeepo]

I wouldn't try the first solution...not on under-ventilated floors on terra= ce houses... The foil under the joist is something I'd like to have a go...the key point= here is RADIANT HEAT - the area around the joists isn't going to be that c= older than the temperature above...if condensation is formed it should drai= n safely on the crawl space. I would pay =A3=A3=A3 to check a real life example of this particular desig= n (aluminium under floor joists)...and why haven't I thought about that bef= ore? nor have I come across any publication/diagram to show this system? Ma= ybe is a new idea? For less than =A340 per room one can solve a very common= plague of suspended ground floors (especially in terrace houses).

[Grimly Curmudgeon]

Conscientious builders used to spray the underfloor soil with a layer of tar to keep the moisture levels down. Adequate ventilation was still needed, of course.