Celotex is not better or worse than any other PIR board it's made from exactly the same basic materials. Kingspan has similar boards with the same insulating properties.
They make different thickness boards and other minor changes for different applications like the relective backings.
There are companies that trade in seconds of these materials, therefore buy what is cheapest to suit your project once you have spec it out but it will steal wallspace in a narrow garage at a fast rate.
In the end I used fibergalass insulation in my garage because after doing the calcs for the garage, I was spending more on insulation using a polyurathane solution than I would save by electricity.
The fiberglass was 25% of the cost and saved 50% of the heat of the polyurathane. Therefore horses for courses.
I assumed 40 days a year working 8 hours a day in the winter. If you are using it on a constant basis the numbers would change. Towards the polyurathane solution
If you want to send me the sizes of your garage by PM, I will do a model for you if you have excel on your computer that will allow you to look at the difference in installation cost and power saving. What fuel are you using electricity or gas.
If you do not have excel I will send you a tex based answer and I can then do various solutions in a table to give you an idea of cost vs saving.
Will it be DIY or will you get a man in to fix it.
