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Types of roofs

Types of roofs

6 Dec 2021

Warm Roof vs Cold Roof vs Inverted Roof

What is a Warm Roof?
A warm roof is where the insulation is above the roof deck and below the waterproofing.

What is a Cold Roof?
A cold roof is where the roof deck is above the insulation. Usually the insulation is fitted between the joists or rafters.

What is an Inverted Roof?
An inverted roof is where the insulation is above the waterproofing layer and above the roof deck.

What are the pros and cons to these roof types?

Roof Type Pros Cons
Warm Roof

Minimises thermal bridging.

Easier to achieve low U-Value due to no limits on timber depth.

Can’t be used where adding extra height to the roof isn’t permitted.

(Alternative Optim-R system can be used for thinner finish)

Cold Roof Filled joist space so no wasted space.

Limited space to fill.

Thermal loss through timbers

Inverted Roof

Insulation placed over waterproofing which protects this layer.

Good for use on a roof terrace.

Has to have a separate waterproof breathable layer to stop the insulation getting wet.

Usually installed with XPS or EPS which is lower Thermal Value so thicker layers are needed.

Warm Roof Cold Roof
Warm Roof
Inverted Roof Inverted Roof - Green Roof
Inverted Roof Inverted Green Roof

How do I install these types of roofs?

Warm Roofs

Warm roofs have two installation methods, mechanical fix or fully adhered solutions.

For mechanical fix we recommend the use of our warm deck fixings which consist of a plastic tube and metal screw. This reduces the risk of any cold bridging. This can be done with a foil faced board such as Kingspan TR26 and/or an upper timber deck. You need a 18mm lower deck and a vapour barrier installed below the foil faced insulation. Its advisable to use a bitumen backed VCL such as ALUTRIX to ensure punctures from the screws self seal.

For a fully adhered system you need to use a fully adhered vapour barrier such as ALUTRIX with FG35 primer. Followed by a tissue faced insulation board such as Kingspan TR27 or Rockwool Hardrock adhered to this with an insulation glue. We recommend Dow Insta-Stik. You can then use a single ply membrane with suitable glues directly onto the tissue faced insulation or adhere a further layer of timber over the top if you want to use an EPDM with a water based glue or a GRP system.

Cold Roofs

For a full filled cold roof you can use insulation boards or wool insulation to fill the joists / rafters.
If you are going full fill ensure that the vapour barrier is fully sealed and waterproofing is sound. If not you will experience damp and rot issues.

For a partial filled cold roof you can use insulation boards or wool insulation to fill the joists / rafters.
When you use partial fill this is usually to allow ventilation of the roof joist area to prevent any damp and rot issues. With this you can use vertical roof vents or soffit vents.
Ensure there is a gap for the roof to breath through the vents.

With cold roofs it’s essential to install a vapour barrier and tape all joints and edges and any punctures. You can use high performance foil vapour barriers and tape for the best results with added insulation benefits.

Inverted Roofs

Inverted roofs are usually installed in commercial applications where XPS or EPS boards are installed over the waterproofing. The waterproofing acts as this and a vapour control layer. You would then install a breathable waterproof membrane over this and then install ballast over the top. Whether this is for example a green roof or paving slabs.

If you need any help deciding which is the best system for you or want a quote for the materials please contact our sales team.