If you’ve found this article, then I guess you’re in the market for a new flat roof or a flat roof refurbishment and are in the process of doing your budgeting, looking for a definitive number to help you decide whether to go ahead with the project or not.
Unfortunately, you’ll be unlikely to find a definitive number anywhere on the internet because there are just too many factors to consider, and we don’t know anything about your flat roof yet.
In this article, however, we will endeavour to give you the next best thing, which is all the information and tools to give you the most accurate estimate of what your particular roof would cost you. We will split this article into three main areas: materials, labour and extra costs. For each area we will analyse the factors of variance and provide ballpark figures for each.
How much do flat roof materials cost?
So, the first thing that will affect the cost of materials is the scope of works. Are you going to have a full warm roof build up or is this just a 2-layer overlay, for example? Let’s break it down.
Warm roof build-up costs
Within a warm roof the biggest variable will be the insulation used. The price can vary based on the type and thickness of insulation used. The two main types of insulation are PIR (polyisocyanurate) and mineral wool with mineral wool being more expensive per m².
Then there’s the waterproofing. Are you going for a bitumen felt, a single-ply or a cold-applied liquid? All these decisions will impact the price. All in all, for a warm roof the materials should cost per m² in the region of £50-£150. This price can increase further with the addition of cut-to-falls or excessively thick insulation.
Cold roof build-up costs
The costs given in this section will apply to both cold roof build-ups and also uninsulated overlays. For example, a liquid overlay to an existing roof build-up that is already up to standard thermally but needs a new waterproofing layer to extend the life of the roof.
In essence, this is the same as the cost of the warm roof but without the cost of the insulation, which, as explained is subject to much variance. The only variable here really is system type. As such, the m² cost will be somewhere in the region of £20-£50.
How much does flat roof labour cost?
The cost of labour will vary slightly based on the specific contractor chosen. As can be expected some contractors are more expensive than others. The biggest variation in labour cost, however, will be the scope of works. Some systems are more labour intensive and time consuming than others.
Although we will revisit this in the next section in more detail, one thing to be aware of is exceptional costs such as scaffolding being included in the labour cost. This can be a significant extra cost, and some contractors may omit it from their labour quote. It is important to compare like for like when analysing quotes so as not to get caught out later on.
Bearing all variables in mind you can expect the labour costs for installing a flat roof to be in the region of £25-£125 per m².
What are the extra costs?
When looking at purchasing a new flat roof or refurbishing an old one, it is important to bear in mind that you will likely not only be paying for materials and labour, although, as mentioned in the previous section some of these costs may be include in the labour cost.
Scaffolding
You’ll need to consider, firstly, whether or not scaffolding will be necessary to access to the roof or as a safety measure. If scaffolding is required it’s important to be aware that the taller the building, the more scaffolding required, the higher the cost.
New deck
Whether you discover the old deck is rotting or you find it’s a fragile outlawed substrate, replacing the deck can be an unexpected and significant uplift. It’s important to make sure of the decks structural integrity when analysing the project. A new timber deck might cost you about £16 per m².
Structural works
If the roof has been leaking, there’s a chance that more than just the deck has been compromised. In some cases, you may have to replace roof joists. In the event that you find a substrate such as RAAC (Reinforced Autoclaved Aerated Concrete) additional structural supports may be required. If you are planning on installing plant on the roof, the extra loading may require the roof to be supported further. A structural engineer should be employed to make sure the necessary protocol is followed.
Waste management
You will likely have to hire a skip for disposal of old roofing materials if you are carrying out a full strip up of the existing roofing system. Hire of a 6-yard skip may cost in the region of £500. Bear in mind that dependent on the size of your project, more than one, or a larger skip may be required.
Get an accurate quote
This article will have given you a decent idea as to how much a flat roof will cost but there’s nothing like an accurate quote. Contact Us today to get a detailed quote specific to your needs.
