We are often asked about the use of insulation boards with solid fuel/wood burning appliances, most commonly freestanding stove installations. This can be a difficult area of work to establish a reliable and usable solution on-site. Our technical helpline is happy to offer advice and this article has been written to provide an introduction to installers where insulation boards may provide a solution.
There are two common applications. They are often used to “tidy up” an existing masonry fireplace recess and also to insulate vulnerable/combustible building components where an appliance is not installed in an existing recess. By vulnerable building components, we are talking here mainly about combustible components of the building structure constructed of wood/timber or simply wall coverings such as paint or wallpaper.
When considering what type of board to use, it is important to consider what guidance there is available to help meet the building regulations, in particular J4: Protection of building.
When being used to simply ‘smarten up’ the interior of an existing masonry fireplace recess that has been constructed in accordance with the guidance in Approved Document J (ADJ), it could be argued that there is simply a need to ensure the board manufacturer approved the product for this application and their method of installation is adhered to. Various paragraphs in Section 2 of ADJ advise that only non-combustible materials may be present in walls adjacent to hearths or within a fireplace recess. Non-combustibility is generally classed as A1 non-combustible in accordance with BS EN 13501-1. There are other descriptions given in ADJ paragraph 31.
In terms of suitable boards that will prove durable when used close to solid fuel appliances, it is the continuous working temperature (or service temperature) that must be considered, but this is unfortunately not always provided in published manufacturers’ specifications. Many boards that are based on gypsum as well as some other compounds will have a service temperature that would be unsuitable for such use.
The service temperature or continuous working temperature may be as low as 49°C
and these types of boards will suffer degradation under long term exposure to the kind of temperatures found next to a solid fuel burner (temperatures in the region of 400°C are not uncommon).
It is therefore important, before starting any installation works, to check with the board manufacturer that any proposed installed materials are suitable for use at the higher continuous working temperatures.
The type of fixing for boards should also be considered as the use of adhesives that might be flammable would be prohibited and it should also be noted that drilling and using screws and rawl plugs in a fireplace recess wall might also compromise the integrity of the structure in terms of its fire protection capabilities.
General alternatives may include some of the cement-based adhesives available on the market. Again, manufacturer’s method of installation must be adhered to
The use of boards to offer protection deemed equivalent to the guidance given in ADJ is challenging. In our experience some boards are not tested under equilibrium conditions to show any equivalence in this sense.
The guidance in ADJ specifies certain thicknesses for masonry or concrete walls adjacent to hearths (around solid fuel appliances) and so not only is the material being used different but may also be of different thickness.
As this is an alternative approach from the current provided guidance in ADJ, to ensure compliance to the regulations sufficient evidence must be available to show that the different method employed provides at least an equivalent level of protection.
We understand that limited testing has been carried out on boards for use in small craft installations (small boats) and there is some guidance reference in BS EN 8511, the scope of which allows application in dwelling installation scenarios.
Further guidance on BS 8511 and guidance on ensuring careful selection of boarding is available from our Technical Helpline team on: 01684 278194.