The easiest way to cut PIR board.
Celotex, Recticel, Xtratherm and Kingspan.
PIR insulation board is yet another way of properly protecting your home. However, when cutting PIR or PUR insulation board it is very difficult to stop the saw from meandering over. It may look good on one side where you have followed the line but when you look on the other side it is either too little or to much which is a bit of a nuisance and does cut the insulation performance down. When working with PIR insulation board you should be always looking for nice, tight fit, however if you do find some gaps around edges-don’t panic! You will fill them with expanding foam.
In this article we will explain you all PIR cutting techniques.
There is many different professional machines like Festool insulation cutter that will give you straight edge each time you cut. What about if you can’t afford such tools? Well, this is where ‘old school’ take its place.
There are 3 methods to cut PIR insulation board.
Method 1 - Cutting PIR with Tame Measure and Stanley knife.
Typically when cutting thick insulation PIR board like most people are use an handsaw. The problem with this is that it does tend to make a lot of mess. When cutting thinner PIR insulation board anything up to about 30-50mm millimeters, you got much better method and is virtually mess-free!
Here is how to do this. This method is clean, quick and simply the best. You don't struggle with a saw at these thicknesses. This made it a lot easier for us over having been using saws for cutting thermal insulation board at this thickness. Pictures show PIR boards made by Recticel but there is many makes out there of thermal insulation board that you can cut using this method.(Xtratherm, Celotex, Kingspan)
This method only refers to PIR boards up to 30-50mm thick.
When you measuring the board with a tape put the metal end at the end you wish to cut. You can use that end of the tape by push it into the board as per below picture.
Now you got marked hole. As you noticed you don't really need a pencil or a knife.
Next step is to mark same way on the other end.
Now you need straight edge. In this case we use spirit level. Secret trick is to use very sharp knife.
Line up your marks, take your sharp knife and just score it gently first of all making sure you get the right line. Last thing is to go back through that line at full depth for the blade. It is easier to do this freehand.
Now very much like cutting plasterboards you turn board over, apply some pressure to one side of the board and just tap and that will now break just as easy as plasterboard. Now you just need to cut along the fault.
You 
will notice from the floor that you got maybe one or two small pieces of insulation board. That is what you want, right?
Method 2 - Cutting PIR with Jigsaw
Lot of people cut PIR board with Jigsaw.
You may find that after cutting long piece, blades gets very hot and the angle of the cut ends go off slightly. However, this method it is still lot easier then using a hand saw. Cutting with standard hand saw will probably give you a straighter cut.
Method 3 - Cutting PIR with Handsaw
When using handsaw you should be really using special saw that has been designed to do no mess and dust. Hovewer some people still say "mess is essentially integral part of your build" Is it really?
Ok, let’s go to the point. When you decided to cut PIR insulation board with normal handsaw get yourself a good nice bit of 2x4 timber!
That will give you cutting line to begin.
When you start sawing you need to keep your saw against the piece of wood and here is the first tip!
Don't go to deep. Just run your saw along that piece of wood keeping it close to the wood and give yourself first cut which will be at 90 degrees. If you keep it saw hard against the piece of timber it means that blade is going down absolutely plumb through the cut.
Next tip is to turn your timber over, line it up, then you run through that cut once more with the timber upright. You simply currying on to that line that you have done allready. This time you go deeper all the way through. Because we are half way through the saw will follow the line!
That way you will get very nice cut out of it.
There is a lot of installers who may say by reading this article "this to much faffing about, I rather do one cut through the board”. Of corse you can, if you are good at it!
If you read this article you most likely doing this for the first time.
This method may take little bit longer but if you are DIYer and if you are doing this for the first time that is definitely the way to go.
Remember, don't be greedy, don’t try and cut one cut in one go because you will find very difficult to keep that saw absolutely at 90 degrees.
We found it easier to do it in two bites!
What happen if I cut PIR boards to big?
If you made those cuts to big you just simply end up slicing bits off for the next half an hour until you can get them to fit which is very time consuming. You better off making slightly too small.
Why PIR boards are marked with lines ?
When working with PIR board you will notice all boards have gauge cross lines every 100mm. This helps to cut boards without straight gauge.
Bibliography
1. youtube.com “Insulation Board Cutting Trick” ,
https://www.youtube.com/watch?v=cqZYMxE0ETI
2. youtube.com “How to cut thin insulation board mess free! Cutting PIR board for beginners. DIY top tip!!”, June 9, 2020, accesed April 09, 2021
https://www.youtube.com/watch?v=5pTfQVzZtkA
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