THE ULTIMATE GUIDE HOW TO CUT FIBREGLASS INSULATION*
Whether you are using insulation rolls or batts, they will have to be cut to size almost perfectly. Importantly, it is the accuracy of the cut that may determine the tightness of the insulation joint. Moreover, inaccurately cut can consequently lead to thermal bridges and thus visible dump on the walls. Therefore it is important that each insulation piece has been cut precisely.
The best way to cut loft insulation rolls or batts will vary depending on what material you are using, with options that are best suited for mineral wool and fibreglass. By the end of this article you will have everything you need to know and all the tools that you need to buy to cut loft roll insulation like a true professional.
TABLE OF CONTENTS
THE ULTIMATE GUIDE HOW TO CUT FIBREGLASS INSULATION
BEST WAY TO CUT INSULATION ROLLS
HOW TO CUT FIBREGLASS INSULATION LENGTHWISE?
LOFT ROLL INSULATION CUTTING GUIDE
2. ROLL OUT THE FIBREGLASS INSULATION
5. CUT FIBREGLASS INSULATION 20mm BIGGER
6. CUTTING LOFT ROLL INSULATION
BEST WAY TO CUT INSULATION ROLLS
Generally speaking, loft roll insulation can be cut physically by a bread knife or mechanically by jigsaw. To cut fibreglass insulation physically, most people use long blade bread knives or machetes. The blade length directly affects the cutting angle as well as the ease of use. The short blade would almost force you to stick your hand through the itchy wool and would shorten blade lifespan very quickly. Therefore, the machete seems to be the best to cut loft roll insulation the more so because its heavy structure itself presses the insulation roll during cutting. Nevertheless, using an ordinary bread knife should not cause too much trouble.
When you are about to install a loft insulation roll on a commercial basis, it would be worth it to use a jigsaw with a spliced blade. It is the fastest and most precise form of fibreglass insulation cutting. Unfortunately, this method requires using very expensive tools such as Festool ISC 240.
Pictrure credit:festool.com
HOW TO CUT FIBREGLASS INSULATION LENGTHWISE?
Most of the loft rolls come perforated in more than one place to suit different joist spacings. However, some of them still come in full 1200mm sizes. Here we need to look for the easiest cutting method. Certainly, this method is different from the others and known as the effortless technique of cutting loft roll insulation.
All you have to do is to NOT take off the plastic wrapper! Using a permanent marker, mark on the width that you want (a few cm bigger than joists) and I cut using a long bladed saw.
LOFT ROLL INSULATION CUTTING GUIDE
1. PROTECT YOURSELF
Fibreglass insulation can cause skin irritation. You should always wear a protective dust mask and safety glasses, to avoid inhaling any fibres or getting them in your eyes. The exception to this is if you’re using sheep’s wool because it’s not an irritant to the skin. Make sure you keep your window open too!.
2. ROLL OUT THE FIBREGLASS INSULATION
Protect cutting area with OSB board.
Unroll just enough to complete the cut you wish to make.
Make sure you bend the loft roll the other way.
Thanks to this, you will achieve a full loft roll dimension.
Lift the roll up and shake well. This way you will get better results.
3.TRANSFER THE MEASUREMENTS
Now you have got a loft roll ready to be cut. Measure the row between the studs where you need to lay your insulation. Once you know what size you need, transfer it to the fibreglass surface with the measuring tape. You can use 3 methods for this. Either by making small marks to indicate where you plan on cutting it, direct small cuts on both edges or by placing wooden straightedge along the line you need to cut.
4. USE APPROPRIATE TOOLS
Fibreglass insulation dulls blades very quickly. For this reason, it will always be easier to cut with a sharp knife.
5. CUT FIBREGLASS INSULATION 20mm BIGGER
It is a good practice to cut fibreglass insulation bigger. Yes, that is right. Even though you need to cut 120cm - cut 122cm. Please note, fibreglass insulation is very flexible. In fact, it can be tucked into tight spots. The extra length will help it stay in place.
6. CUTTING LOFT ROLL INSULATION
Make sure the board is perpendicular to the insulation and up against both marks you made. It can slip out of place, causing the insulation to look uneven after you cut it. Put spirit level against marked lines. Press the spirit levels and cut the wool with the greatest force.
Remember to hold the blade at an angle. This will ensure a nice cut and will not tear the edges.
After the first cut, open the cut area and cut again.
You will probably feel that you are cutting the OSB underneath. That's good!!. This means that you definitely cut the wool this time.
Shake cutted piece of loft roll once again. This will allow the wool to fill fully. ‘Pumping’ loft roll is one of the most important steps. Every inch of inflated roll equals every inch of insulation.
Now you are ready to fit loft roll.
Repeat all steps till you finish roll. Keep small off cut for small areas such corners or awkward places.
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