Insulating external balconies

Firstly, Dear Reader, an apology. The thick book has had to be brought into use this last month due to an authoring error.  As correctly pointed out, all WFRL’s are not made equal, they are in fact made out of different materials from different manufacturers; not a single material from a single manufacturer as stated in error last month.  

Now to get off the naughty step and focus on this month’s topic; Insulating external balconies.

We have covered the need for non-combustible (class A1 or A2, s1-d0 to BS EN 13501-1) insulation on balconies in a few columns, so you will be pleased to hear we are not going to ‘teach you to suck eggs’ this month.

Hands up how many are reading this thinking “a balcony is over air so it doesn’t need insulation”? In some cases, you would be correct for thinking we had lost our marbles, but there are balconies that are over air and still need insulation, such as cantilever balconies where the floor slab extends through the external wall to create a projecting balcony. This will certainly need insulating to prevent a cold bridge into the apartment, and yes it will need to be non-combustible (sorry).

Other forms of balcony that bolt to the structural external wall can require insulating, although the insulation may not have to extend the full depth of the balcony (away from the external wall). Again ‘that word’ non-combustible (sorry #2) comes onto play.

Of course, balconies over heated space always need to be insulated with an insulation product that doesn’t burn (yep, another way of saying ‘non-combustible’; sorry #3).

The biggest consideration when choosing your non-combustible (#4) insulation is going to be long-term compressive strength, as let’s not forget the main purpose of a balcony is for people to actually use it to stand on, and many will have table and chairs added to them. Gardeners will be putting planters on them, some will grow vegetables on them and others may put a hot tub on them. In every application, except probably the last one, the surface load will be transferred through the surface finish via paving supports and/or paving supports and rails, creating a point load where the support meets the waterproofing or insulation surface.

The best solution to insulate a balcony, in our opinion, is FOAMGLAS. We have seen solutions put forward that involve Mineral Wool/Stone Wool with a CP Board over the surface to load spread. Now, we love Mineral Wool/Stone Wool for non-combustible non-trafficked roofs, but this application is not BBA certified nor tested to EN 1606:2013 Thermal insulating products for building applications – Determination of compressive creep.

Remember, the diameter of the paving pedestal (and its strength) will impact the load spreading, so the larger diameter the better.

Next month: The value of VIP Insulation boards