CELOTEX TIPS AND TRICKS

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hi all,

I write this a broken man. I am currently 12 months into building a 4 bed dormer bungalow. I have been involved a great deal from the wind and watertight stage. i.e carpentry, electrics, plasterboard and insualtion etc. I am living on site in a caravan so I get the convenience of early starts and late nights. Its been enjoyable so far.............. Until.... CELOTEX!!!!!!!!

I have trawled this site again and again looking for hints and tips on the installation of it and I cant find any.

This is the closest I have been to admitting failure so please someone tell me that this job can be done without me taking my blood pressure to extremes.

Best way to cut it
how to get absolute accuracy...I cant live with the gaps if I measure to small
install it in 8' or 4' lengths
Do I insualte the full length of the rafter or can I insulate the upstand supporting the rafter - fed up crawling into the dead space to try and fit it.

Any other hints and tips would be appreciated
Oh, and I had planned to use tri iso quilt but at the last minute the
BC said that it has to be used with 70mm celotex aswell to meet the regs - whats the point in that - the whole idea behind tri iso I imagine was the massive labour saving compared to Celotex. Anyone else heard of this


thanks
 
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I have used an old hand saw or Knife for cutting Celotex, it's very quick and accurate. As for info on installation, have you looked at the installation publications on the Celotex Website Here.

Salem.
 
thanks salem

Ive been on their website before i started

they recommend measuring accuratley , then cut at a slight angle to achieve a friction fit.

the downside with this principle is that the baord you are left with is oversized on one side due the the angle. - or am i missing something
 
Tri-iso can't usually be used in rooves (on its own) , its not certified, very common nowadays unfortunately.
 
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phil01 said:
thanks salem

Ive been on their website before i started

they recommend measuring accuratley , then cut at a slight angle to achieve a friction fit.

the downside with this principle is that the baord you are left with is oversized on one side due the the angle. - or am i missing something

I just make a square cut, measure twice, cut once. If it is a good fit but no friction to hold in place, use a couple of small nails tapped part way into timber to hold it. to ensure that the 50mm air gep was not compromised we fixed a 50mm x 25mm batten to the timbers prior to installing the Celotex. A vapour barrier was then fixed before the plasterboard.

We have two 80mm layers of this in our loft conversion, I would say 50% is held in position this way. As for which way to cut "Width or Length" it's all down to what you can handle without any hastle.
 
good so far.......

Another problem I have is that there are discrepancies in the width between the rafters.

I can measure at one point i.e 362mm

then further down the rafter at say the 1200mm mark it measures 400mm

whats the best solution to this - cut the biggest gap or smallest. I don't want to cut to the actual measurements as this will leave the board i am cutting from uneven.

sorry to keep bringing up problems

many thanks for the advice
 
In case it's helpful - I helped my builder build my extension last year and we used this INSTA-STICK (http://www.geocel.co.uk/product.aspx?id=206&pt=diy) adhesive foam to stick 100mm foil backed XTRATHERM boards direct to the new thermalite block solid walls. We then fixed battons to the XTRATHERM board then foil backed plasterboard. The INSTA-STICK product has been so useful, I use it all the time now instead of dot-n-dabbing plasterboard to any surface, it's very strong and sets within a few minutes so you don't have to hold boards in place for very long. Kevin
 
Cut the board [ends] square to the measured width, and then when you place them in, if they are a bit oversize or tight, then run a handsaw down tight against the rafter while they are in place, and then push them in.

For gaps, the slivers which were cut off, can be wedged in.

For uneven widths, don't cut the board square, but cut it to the measured sizes.

Don't forget your mask, goggles and paper overalls - the dust is a nightmare

You can buy Xtratherm insulation which is actually precut with lots of slots, so that it can be squashed together to go between the rafters, and it then springs out to make a tight fit
 
Hope this helps, I finished fitting between rafters ecotherm (basically same stuff) a few months ago. Albiet I fitted before battening and used a jig to set rafter spacing, which made life a lot easier. I like salem used battens 38x25 to get the depth right.

If your rafters are (were) pretty stright and only give a variance in width because of instalation, I would measure the gaps between rafters in three places. If using 8' boards that would be 4' intervals, top middle and bottom. I would say the larger the better it means less handling and joints.

Then for instance, if you have 2 which differ by 20mm ie 380 top 400 bottom you can straight cut one, spin the board round and cut the other. I found that the ends were so close to 90degrees it wasnt worth worrying about. This saves on cuts and material and youre still left with a straight (non tapered) length to cut the next one from.

I then used one of my wifes steak knife (as its serated) to scrape off any excess if they were oversize. This helped to give a push fit with no gaps. I was also told that expanding foam could be used to seal up any gaps.
Not sure what you mean by upstand?
NB It takes a long time.
 
I am working on my extension at the moment, and and am sharing what I have learned so far.

Background: I am using Celotex XR3000, at 120mm, to insulate the external walls of my first floor timber-frame extension. I bought it using a best price policy from www.bmdinsulation.com, who delivered within two days and were genuinely cheaper.

Celotex is very large, so if there is someone to hand to help you, do so!

Cutting:
I used a tapemeasure, a normal (but sharp-toothed) saw and a stanley knife. I cut a marking line using the stanley knife. This helped to not tear the foil backing when sawing. My instruction use was to have the printed side face outward (plain side facing the air cavity), so I found it easier to cut from the plain side (as it is very hard to cut this depth of celotex completely 'true').

Fitting:
Wear the mask and goggles - you really will need it, especially for the fitting! I measured to the nearest .5cm, which made fitting easy, as almost all blocks ended up being friction-fitted. In a sealed space, the main difficulty you'll have is actually allowing the air out of the space you're putting the Celotex in!
I used a block of wood and a rubber hammer to put the celotex into the space. Offer up the celotex, to see it is the right piece and fits well - then push it into place, then use the block/hammer to gently fit it into space.

If it is not going to fit, trim some of the leading edge off (the first bit going in), to give yourself a fighting headstart!

After a while, I was confident enough to cut several pieces at a time, but it is worth sitting down beforehand with all your measurements and working out the right layout for your cuts on each board. By doing this, I reckon I saved a fair bit of money on a 'safety' board, for those extra's I hadn't accounted for!

I hope this helps!
 
the downside with this principle is that the baord you are left with is oversized on one side due the the angle. - or am i missing something
You could try turning the board over before cutting the next strip (still working from the cut edge). That way the angle works for you rather than against you. I'd turn it side to side rather than top to bottom so the tolerances tend to cancel out rather than adding up.

In the long run, I doubt it matters which foil faces the cavity. There is only a slight difference in emissivity due to the printing on one side. Facing upwards next to a vented cavity, I think the foil will get dirty quite quickly and increase the emissivity anyway. As the foil gets dirty, I suspect the R value of the reflective vented cavity will gradually drop from possibly 0.47 (SI units) down towards 0.18 for a non-reflective cavity.
 
hi all,

I write this a broken man. I am currently 12 months into building a 4 bed dormer bungalow. I have been involved a great deal from the wind and watertight stage. i.e carpentry, electrics, plasterboard and insualtion etc. I am living on site in a caravan so I get the convenience of early starts and late nights. Its been enjoyable so far.............. Until.... CELOTEX!!!!!!!!

I have trawled this site again and again looking for hints and tips on the installation of it and I cant find any.

This is the closest I have been to admitting failure so please someone tell me that this job can be done without me taking my blood pressure to extremes.

Best way to cut it
how to get absolute accuracy...I cant live with the gaps if I measure to small
install it in 8' or 4' lengths
Do I insualte the full length of the rafter or can I insulate the upstand supporting the rafter - fed up crawling into the dead space to try and fit it.

Any other hints and tips would be appreciated
Oh, and I had planned to use tri iso quilt but at the last minute the
BC said that it has to be used with 70mm celotex aswell to meet the regs - whats the point in that - the whole idea behind tri iso I imagine was the massive labour saving compared to Celotex. Anyone else heard of this


thanks

The easiest (though not the cheapest) way to ensure a good fit, without lots of cutting and recutting, is to cut 1/2 inch undersize, and foam around the edge with expanding door and window fixing foam, which is both low-expansion and waterproof. This glues it to the timber. On a vertical surface, the Celotex should support itself while the foam goes off; on a overhead slope, it'll need temporary fixing on the skew with nails or screws.

My BCO wanted 5 inches for our bungalow loft renovation, which I did as 4 inches between the rafters (after battening out to 6 inches) and one over. When fixing with PB screws over the 45 degree rafter section, I found the heads tended to pull through the foil backing (this with 25mm Celotex; the foil backing on Kingspan I found to be more robust). So I used gaffer tape as washers for the screw heads.

Once foam has gone off, the Celotex boards are going nowhere. You can smash your fist into Celtoex foamed into studwork, without budging it.

Cheers
Richard
 
hi all,


Do I insualte the full length of the rafter or can I insulate the upstand supporting the rafter - fed up crawling into the dead space to try and fit it.

Second reply, sorry: I don't see why you can't insulate the upstand, as long as the insulation and vapour barrier (foil and tape) is continuous on the room side.

If part of the ceiling of a room below is under the cold side of the upstand, you might want to insulate with some loft insulation, to avoid heat loss from the room below - making sure you don't block your airflow from the eaves into the ventilated space behind the Celotex in the rafters (assuming one is required for your type of sarking).

Cheers
Richard
 
Hi

Ive been struggling with celotex for several months renovating a bungled loft extension. The original builders diddnt bother to put any insulation in at all in some places so I have had to rip all the plasterboard down and start again.

My first plasterers offered to fit the new celotex but they were rushing it and leaving huge hidden gaps behind rafter joints...so I opted to do the work myself slowly and properly.

Its been a struggle and I've learned from my mistakes so here are a few tips for anyone starting out;

Firstly WEAR THE RESPIRATOR! very important.... celotex is non toxic but the dust gets in your lungs and will cause irritation. The foam may contain some 5% of glass fibre threads and as with rockwool you dont want to be breathing it.

(I'm now being treated for Bronchitis but I know my respirator leaked on one day so I'm probobly reacting to the dust.)

Celotex can be cut with a knife but that can be a bit wibbley wobbley...a fine handsaw with a wide blade gives the most accurate cuts and not too much dust. there are special celotex saws available which are not too expensive.

I opted not to use a knife to reduce dust as you end up shaving the stuff down anyway as you fit it and the dust still gets everywhere.

If doing rafters, consider using two thinner sheets i.e. a sandwhich of two 50's rather than a 100mm sheet. works out a bit more expensive but is far easier to cut in and the extra time in fitting two layers probobly matches the time lost in otherwise accurately cutting thicker panels.

There may also be some thermal benifit in having the extra 2 aluminium sheets that you wind up with.

I cut each panel about an inch wider than the rafter making sure there is one streight edge. I slice these panels from the width of the sheet so they are four feet long. I have found that if you offer one edge up to the side of one rafter, you can bang on the other side so the wood crushes the edge of the oversise celotex a little. You can then use this line as a cutting guide.

For very knobbly rafters I use the same technique but overlap the celotex slightly rather than offering it up to the first rafter. I them 'bang in' mark the other side, cut it to shape and then offer that edge to the rafter it was measured against. You can then and 'bang in' mark and cut the other side for a perfect fit.

I plug any gaps with slivers of celotex as I cant use foam... there is no roofing felt on my old roof so foam would simply squirt up between the tiles.

regardles to what some say the dust is nasty... please buy a good respirator...I used what turned out to be a a crappy one from amazon and as I mentioned the rubber allowed dust to leak past the mask.

I've been coughing for 3 weeks now, maybe I have got bronchitis but two courses of antibiotics have not cured it. I blame the Celotex dust.

Hope this helps someone.
 

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