Upgrading Fire Doors – So many people ask us if they can upgrade doors to comply with fire door regulations,
and our answer is always…

Yes this can be done…


The door needs to be at the very least of the correct type and thickness. Thin modern (eggbox filled) panel doors normally cannot be upgraded, but if you have a good solid period oak door it probably could be, and of course there is a vast range of doors in between. Each door therfore must be assessed for potential suitability.

Due to the hugely varying nature of doors and their construction, it is impractical and misleading to carry out NAMAS / UKAS Fire Test Laboratory fire door testing.

So… please read the two documents below – and show them to your local Building Control Department. If you still have questions or need more help and advice please call us.

Upgrading Internal Doors to 30 Mins Fire Resistance with Timbercoat Intumescent Paint

Most modern normal internal doors cannot be upgraded to achieve 30 minutes Fire Resistance.

The issues are they often have a hollow core, can be very thin, lightweight and are liable to warping shortly after installation. No door answering such a description can be upgraded and should be replaced with a new Fire Door where one is required.

While we recommend the installation of custom-built fire doors there can be reasons not to do so.

Doors that Timbercoat is capable of upgrading are ones that can afford to lose 2mm to charring.

  1. Solid, joint-free doors with compressed core and a reasonable thickness (6 mm + ), veneer faces bonded to either side of the core. These can be flush doors or pressed to create a moulded look.
  2. Seasoned, old or sturdy doors with 35mm +thick frames and solid panels 10mm + thick.
  3. Certain other doors that are not prone to premature collapse.

Note- Well seasoned or old, sturdy doors with panels 8mm thick can be upgraded if addition “sacrificial” ply panels 6mm thick are fitted in the panel recesses and held in place by the door’s beading.

If your doors are in a category which could be upgraded submit your assessment to your Authority, along with this explanatory Technical Note for approval prior to purchase. Thermoguard UK will issue a Fire Certificate for Authority approved projects following completion.

Our recommendation is that both sides of the door are protected and we are unable to supply certification unless sufficient product is purchased and applied to both sides of the door.


As doors vary so greatly and the great majority are unsuitable for upgrading it is neither meaningful or realistic to carry out an official NAMAS / UKAS Fire Door Fire Test.

Thermoguard Timbercoat’s uniquely effective formula resulted in the UK’s only successful official UKAS / NAMAS Fire Test Laboratory Fire Resistance Test to 60 minutes on softwood with timber lost to charring restricted to 7-10 mm at 60 minutes ( unprotected softwood charring is approximately 50mm ).

The system was also demonstrated by the Megastructures TV documentary “Building from Disaster”.

Charring was restricted to 2mm and integrity and insulation were retained throughout a 45 minute maximum severity burn (more severe than BS 476 part 22).

This was while identical unprotected panels burnt in parallel were shown to burn through completely within 6 minutes.

Thermoguard Technical Department assess doors as suitable based upon the customers description, which features on the Fire Certificate issued, so this information should be checked before ordering.

We require that in a fire the door be capable of losing 2mm plus 2mm additional safety factor to charring without the risk of splitting or cracking of the thinnest areas (usually the panels) or other premature failure, while maintaining insulation.


Apply 4 coats Thermoguard Timbercoat @ 7 sq m per litre per coat.(Timbercoat data sheet).

Then apply 2 coats Thermoguard Flame Retardant Paint.

We recommend Astroflame intumescent strips are fitted around the door edges or in door casings.

Coverage Timbercoat 5 Kg 2 doors. Flame Retardant Paint 2.5 litres 6 door sides.

Advice. Fire resistance depends on the chosen coating’s performance on the type of material the surface to be protected is made from and that surface’s thickness and construction. Fire performance of clear fire coatings and that of coloured fire paints (which are far more effective in increasing fire resistance) and performance on surfaces varies dependent upon the surface.

Modern building materials often have little in common with similar named historic forerunners (a particular case in point being lath and plaster) and, though not clear from some manufacture’s literature, tests on coloured paint fire coatings are not relevant for their clear fire coatings.

It is therefore advisable to obtain confirmation of the fire test evidence any manufacturer proposes to support the use of the particular chosen product and pass this to your Authority to consider the relevance of the surface and materials tested to your particular case and the actual test results.


Fire Resistance to Doors using Fire Varnish and Fire Varnish Overcoat

Please refer this to the appropriate Authority for approval before proceeding.

Due to the hugely varying nature of doors and their construction, it is impractical and misleading to carry out NAMAS / UKAS Fire Test Laboratory fire door testing. Each door must be assessed for potential suitability.

The great majority of doors, including all hollow doors, are unsuitable for upgrading to 30 or even 20 minutes Fire Resistance.

There are, however, certain well constructed, solid and substantial doors capable of being upgraded with our Fire Varnish intumescent as this is by far the most effective clear fire treatment or coating available.

Generally suitable doors are hardwood or solid with hardwood veneer.

Intumescent paint ( white or coloured ) is capable of significantly greater Fire Resistance. If you have softwood doors we suggest you refer to our “Fire Door Paint” information page.

Our Fire Varnish Class O Part 6 Fire Propagation Test indicates the protected softwood did not burn within the 10 minutes test duration. Further in-­-house testing indicated that when applied at twice the Class O spec. . Thermoguard Fire Varnish intumescent added 15 minutes Fire Resistance. To add a degree of “leeway” we specify that it be applied at aprox. three times the Class O spec.

We assess projects requiring 30 minutes Fire Resistance on an individual basis, referring to the TRADA Char Rate Tables and calculated residual timber to ascertain whether we could issue a Fire Certificate for the project. In order to enable us to issue a 30 minutes Fire Certificate in the case of softwood the surface must be able to afford the loss of 10 mm depth from all surfaces exposed to a fire.

In the case of oak or similar woods the loss to take into account is 6 mm.

In other words, the residual timber should be adequate, after such loss in the case of a door to avoid premature collapse, splitting or cracking ensuring neither flames or the substantial heat required to promote combustion can pass through the door. .

Pine and Other Softwood:
In general terms few modern softwood doors can be protected with confidence.

Old and hence very well seasoned softwood doors can be protected but only if the frame can withstand 10mm loss.
In these cases panels less than 16 mm thick should be supplemented by inserting an additional panel to make the total panel thickness 16 mm. trapping the additional panel behind the door’s beading.

Substantial, solid doors unable to afford the loss of 10 mm to the frame can achieve 20 minutes with the 30 min spec as below provided they can afford the loss of 4 mm.

Oak and Other Resistant Hardwoods including modern doors with solid compressed cores and 6mm oak veneer faces.

These doors with frames 35 mm + thick can be upgraded to 30 minutes. Any inset panel less than 12 mm thick should be supplemented by an additional panel trapped by the door’s beading to take overall panel thickness to 12 mm +.

Door Surrounds & Seals: 
We recommend the gap or joint between the architrave and wall is sealed with Intumescent Mastic after application of Fire Varnish & FV Overcoat, so your order should include for intumescent mastic. We also recommend that intumescent strips are fitted in the door jambs and to the underside of the door.

Specifications & Order Quantities:
30 Minutes Fire Resistance Specification ( 20 minutes in case of some softwood doors as referred to above )

3 coats Thermoguard Fire Varnish @ 7 sq m / litre per coat
2 coats Fire Varnish Overcoat – matt , satin or gloss

COVERAGES 30 / 20 minutes (as above) allows for the number of coats necessary

20 sq m pack Fire Varnish = 2 doors & surrounds

Plus 20 sq m. Fire Varnish Overcoat = 2 doors & surrounds

Plus 1 tube Intumescent Mastic