Floor insulation with a ventilated crawl space

[manzana]

Hello,

I live in a Victorian house (very early 1900's) and the floors are not insulated, which makes the downstairs noticeably cooler than upstairs. Currently it is fully carpeted downstairs which is all brand new when we bought it, but when carpet gets older we plan to change to engineered hardwood floors in years to come. However, I would like to insulate asap and have a couple of questions below.

1) Which is the best way to insulate the floor? From underneath by getting into the ventilated crawl space or from above by lifting floor boards?

2) Should I seal all of the air vents in the crawl space, making it unventilated? I have been advised to do this by people I know.

3) What insulation material(s) should I use?

4) Is it a diy job or should I get a tradesman to do it? If so, any recommendations?

5) Anything else I haven't considered?

Thanks for all you help and time in advance!

 

[freddiemercurystwin]

1) If the crawl space is adequate then this is far less disruptive and messy to do, lifting carpets, floor boards is gonna be horrendous though of course if doing from the underside it’s not fun if the space is only 1 foot or two.

2) Absolutely not. Never ever block up the vents that vent the void beneath the floor. Those giving you this advice are completely wrong.

3) There are basically two methods, have a read of my post in this thread: //www.diynot.com/forums/floors-stairs-lofts/insulating-ground-floor.334961/#2492345

4) Whilst it is fiddly and messy it can be easily DIY’d and arguably you will probably do a much better job than any tradesman as (seeing as it’s a bit of a grim job) most tradesmen who will be prepared to do take on such a crappy job probably won’t be very good.

5) You’ll need some goggles and probably some masks. Just in case you missed it, do not block up any vents!

 

[geraldthehamster]

Unless you're blessed with a comfortably deep space under the floor, you will be faced with either lying on your back while rock wool, Celotex crumbs or expanding foam falls into your face, or taking up all the floorboards and doing it from above, which is a bit disruptive.

I did the latter in my ground floor, as the space between joist and oversite was only about a foot. I put the boards back after sanding them, but some were the worse for wear.

The method I used was to fix 50mm Celotex between the joists with exanding foam. This gives the best seal against draughts.

The alternative is to hang rock wool between the joists on chicken wire, or plastic mesh.

As has been said, whatever you do, don't block any of the air bricks to the under floor space.

You'll find plenty of posts on the topic if you search the forums for "floor insulation".

It's worth doing.

Cheers
Richard

 

[manzana]

Two fantastic replies!
Thanks guys.

 

[manzana]

Hi Guys,

Just measured and the crawl space height is roughly 90cm.
So enough space for me to get down there as its nice and dry.

I will definitely be doing it from the crawl space (less disruptive) and I read the two options available. Can I use Celotex if doing it from underneath? Or is Celetex only used if lifting floorboards?

Also, which is normally cheaper; celotex or mineral wool?

Cheers!

 

[freddiemercurystwin]

Mineral wool is definitely cheaper, but then is less resistant to the passage of heat, meaning you need more of it to achieve the same result. There is nothing stopping you using Celotex from the underneath, you will just have to push them up, squidge some foam into any gaps and then either fit battens to hold them or pop some small nails in to hold them up. It will be awkward to cut the sheets and get them in, but then fixing chicken wire for mineral is hardy a joy to do. Personally I would recommend to go the Celotex route.

 

[geraldthehamster]

Hi Guys,

Just measured and the crawl space height is roughly 90cm.
So enough space for me to get down there as its nice and dry.

I will definitely be doing it from the crawl space (less disruptive) and I read the two options available. Can I use Celotex if doing it from underneath? Or is Celetex only used if lifting floorboards?

Also, which is normally cheaper; celotex or mineral wool?

Cheers!

It's probably easier to use rockwool if working from underneath. Maybe someone who has done this can advise. I guess you would use either chicken wire or perhaps garden plastic mesh, squidge the rock wool between the joists, and staple the mesh under it as you go. Try searching the forum.

I've not tried fixing Celotex from underneath, though I'm sure you could. Expanding foam is commonly used to seal it to the joists, and I might be a bit wary of using foam in a confined space due to the fumes. And you definitely don't want it dropping on your head. You could just cut the Celotex as accurately as possible and support it on nails of screws driven sideways. Celotex isn't very forgiving if you try to shove it in, oversized.

Rock wool is cheaper than Celotex.

Cheers
Richard

 

[geraldthehamster]

Mineral wool is definitely cheaper, but then is less resistant to the passage of heat, meaning you need more of it to achieve the same result. There is nothing stopping you using Celotex from the underneath, you will just have to push them up, squidge some foam into any gaps and then either fit battens to hold them or pop some small nails in to hold them up. It will be awkward to cut the sheets and get them in, but then fixing chicken wire for mineral is hardy a joy to do. Personally I would recommend to go the Celotex route.

Sorry, hadn't read this before replying. I agree that Celotex is better in principle. As I said, I haven't tried rock wool.

When cutting Celotex, do it as accurately as possible and don't assume that all your joist spacings are the same until you've measured them

Cheers
Richard

 

[manzana]

Once again, some very informative replies!
Thanks!

 

[manzana]

Hi Again,

Doing my research as we speak, I came across something called Earthwool . http://www.insulationshop.co/75mm_e...l_knauf.html?gclid=CJTg-vDcj78CFejHtAodqSMAVg
Is that the same as Mineral Rock Wool you mentioned?

Also, seeing as I need to use more rock wool to get the same thermal protection as celotex.
Would a 75mm wool give similar protection as 50mm celotex?

Leaning towards rock wool as it may be easier to work with and also no expanding foam falling on me.

 

[JohnD]

a good thing about mineral wool is that it is somewhat compressible, so you can stuff it tightly into gaps to block draughts. This is especially important round the edges of the room.

As it is permeable it will allow slight ventilation through to help avoid damp.

Get yourself a builders vac and a dustpan and brush, there may be a lot of old rubbish underneath. Especially remove timber offcuts and any organic material as it can harbour rot.

Brush out the dirt and cobwebs that will be blocking your airbricks

Insulate underfloor pipes (usually radiators) with regulations grade climaflex or similar.

Electric cables can touch insulation (but not polystyrene) but must not be buried or surrounded by it. Preferably tack cables to the underside of joists with the quilt supported above so it can't sag onto them. They must have free air on at least one side to prevent overheating.

You may like to provide a hatch to facilitate future underfloor work. In a corner away from the door will be easiest to lift the carpet.

 

[JohnD]

p.s.

get the mineral wool that is treated with Ecose (It is brown not yellow) which prevents it shedding dust and fibres, and it is softer to handle. It makes a tremendous difference, especially in a confined space. It is made by Knauf, but is also sold as own-brand by Wickes and I think B&Q. "Ecose" will be on the packaging, even if own-brand. I would not use plain fibreglass again.

 

[geraldthehamster]

p.s.

get the mineral wool that is treated with Ecose (It is brown not yellow) which prevents it shedding dust and fibres, and it is softer to handle. It makes a tremendous difference, especially in a confined space. It is made by Knauf, but is also sold as own-brand by Wickes and I think B&Q. "Ecose" will be on the packaging, even if own-brand. I would not use plain fibreglass again.

Fibreglass and rock wool aren't the same thing. I agree with you about the fibreglass - I used it in my loft space because I got some cheaply - it's nasty stuff.

Cheers
Richatrd

 

[manzana]

Hello All,

I have decided on using wool.
What thickness is usually recommended?

I have seen; 50mm 75mm 100mm and even 200mm.
Which one should I use that will not later make me wish I had used the next thickness up?

Thanks!

 

[JohnD]

100mm will be plenty and is widely available. Heat loss through floors is not great compared to ceilings, it's mostly draughts.