Once the existing doorset has been carefully removed, you finally get to see what you’re actually working with.
This is the point where I want to forget what the drawing says for a minute and look at the actual opening in front of me.
A new doorset can be manufactured extremely accurately, but the building it’s going into might not have been built to anything like the same tolerance.
We’re now working to 1 mm and sometimes even 0.5 mm, while brickwork, plastering and drylining aren’t necessarily being carried out to those sorts of margins.
That’s why checking the opening properly is so important.
Measure the Opening at Multiple Points
I don’t measure the opening once and assume that’s the size.
I measure at the top, middle and bottom.
If any part of the opening looks narrower or different, I’ll take additional measurements there as well.
You can have an opening that looks reasonably consistent but changes enough over its height or width to cause problems when you’re trying to install a precisely manufactured doorset.
This is particularly common in older buildings.
I’ve seen old doorsets that were measured incorrectly, resulting in a smaller doorset being manufactured and installed into an opening that could actually have taken a much larger one.
🟧 Professional Tip
Don’t measure the opening once and call it done.
Top, middle and bottom are the minimum checks.
If something looks different, measure it.
The opening is telling you what it is — don’t make it what you expected it to be.
Measure the Wall Depth
The width and height aren’t the only dimensions that matter.
Measure the depth of the wall.
You need to know whether the frame you’re installing will actually cover the wall properly.
Older plastered walls can taper or vary considerably in depth. You might measure one part of the wall and find something completely different a little further along.
If the depth isn’t consistent, take measurements at the relevant points rather than relying on one figure.
I would generally rather have a little extra frame depth where appropriate than discover I’ve got a frame that doesn’t quite cover the wall.
For example, adding around 5 mm to the frame depth can sometimes be much easier to deal with than having to spend a lot of time planing the back of an architrave to make it fit.
A small difference can often be concealed behind the architrave with an appropriate finish, whereas trying to make a frame that’s too shallow work can create considerably more work.
Older Walls Rarely Behave Like New Ones
This is particularly noticeable in old buildings.
Walls that have been plastered and repaired over many decades don’t necessarily have a consistent face.
You can have:
- varying plaster thicknesses
- tapered reveals
- uneven brickwork
- previous repairs
- layers of old finishes
- different wall depths around the same opening.
Don’t assume the wall is straight simply because it looks straight from a distance.
Measure it.
Check the Opening for Plumb, Level and Square
The opening needs to be checked in three dimensions.
Is it:
Plumb?
Level?
Square?
Being square can be a rare thing, even with relatively modern stud work.
Dryliners can be working to perfectly reasonable building tolerances while we’re trying to install a doorset that needs much tighter geometry.
That’s one of the differences between the construction around the doorset and the doorset itself.
I use levels for checking the head and lasers for the rest where appropriate, although I’ve used a long level for years.
Even a shorter level can be useful if you hold a properly machined straight edge against it to extend the distance you’re checking.
Older Methods Were Different
Older doorsets were often installed using methods such as plumb bobs to establish the vertical position of the frame.
The head could then be set using a triangular piece with a centre mark to transfer the plumb position.
I’m quite glad we don’t have to do that anymore.
We’ve got much better tools available to us now.
But the principle hasn’t changed:
You still need to establish where the frame actually is in relation to the opening.
What If the Wall Isn’t Plumb?
This is where experience and judgement come in.
As a joiner, I was taught that if the existing wall is badly out, there can be circumstances where you follow the wall rather than trying to make everything perfectly plumb.
That doesn’t mean deliberately installing a badly positioned doorset for no reason.
There are situations where the geometry of the building means a slight adjustment can improve the actual operation of the door.
For example, if the floor rises towards the door and the door is going to catch when it opens, leaning the frame can sometimes help prevent that.
A small change at the top can produce a larger positional difference at the opposite corner over the height of the frame.
But this needs to be a considered installation decision, not an excuse for a badly installed frame.
The doorset still needs to be installed in accordance with its manufacturer’s requirements and tested arrangement.
Old Floors Can Be Surprisingly Difficult
The floor can be just as important as the opening.
Older buildings often have timber floors that have been walked on for decades.
Over 50, 80 or 100 years, timber floors can naturally develop bows and changes in level.
You might measure a threshold and find approximately 7 mm at the jambs, but 12 mm in the middle.
That’s a significant difference when you’re trying to establish the correct clearance underneath a fire door.
You need to understand what the finished floor is doing before deciding where the doorset needs to sit.
Depending on the particular doorset and its tested arrangement, the solution may involve the doorset position, threshold arrangement or an appropriate drop seal.
Don’t simply assume that the floor is flat.
Check the Finished Floor Before Installation
The manufacturer’s required undercut needs to be known before you commit to the installation.
The final floor could be:
- carpet
- carpet and underlay
- vinyl
- tiles
- another floor covering
- or a combination of finishes.
The required clearance can differ depending on the particular doorset and floor arrangement.
If the final floor finish hasn’t been installed yet, you need to establish what the finished floor level is expected to be.
The Falcon installation guidance specifically states that the doorset needs to be manufactured with an undercut suitable for the final floor finish, including carpet, underlay, vinyl and tiles.
And if the doorset is intended to provide smoke control, don’t assume the same clearance arrangement automatically applies. Check the manufacturer’s tested requirements for that specific doorset.
Look for Obstructions
The opening itself might be correct, but something around it can still stop the door operating properly.
Look for things such as:
- skirting
- radiators
- pipework
- thresholds
- floor coverings
- furniture
- adjacent walls
- other doors
- restricted areas around the opening.
This is especially important in older buildings where rooms and openings may have been altered several times.
A doorset can fit the opening perfectly and still have a problem when you actually open the door.
Check the Fixing Positions
The opening might be the correct size but still not give you ideal fixing locations.
Where the fixing points aren’t the best, in rare circumstances I’ll place the frame into the opening and mark the actual fixing positions directly across onto the frame.
That allows me to work from the real opening rather than assuming the fixing positions will work exactly as planned.
If the opening is particularly bad, you may have to plan the fixing positions carefully.
In exceptional circumstances, structural reinforcement may need to be added to create a suitable fixing point.
That’s not something I regard as normal practice or something to improvise. It needs to be appropriate to the wall construction and the manufacturer’s fixing requirements.
The Falcon guidance specifically requires structural reinforcement to be present where necessary and capable of providing suitable screw retention.
Check the Stud Wall Properly
Don’t just look at the plasterboard.
On stud walls, check what is actually behind it.
I’ve come across situations where the wall construction hasn’t been properly secured to the floor.
There’s no point trying to install a precisely manufactured fire doorset into a wall that can move from side to side.
If the stud wall moves when you start tightening the frame fixings, you’re going to struggle to get the frame where you want it.
If necessary, the wall construction needs to be properly secured before the doorset is installed.
The same principle applies to timber stud construction.
Check for movement before you fix the frame.
Don’t Fix Into a Poorly Constructed Metal Stud Wall
I’ve seen metal stud walls where timber or plywood reinforcement has been fixed to the outside of the metal stud, rather than being incorporated correctly into the stud construction.
This can cause problems when you fix the frame.
As the frame fixing is tightened, the reinforcement can pull the metal stud in a way that draws the construction apart.
You can then get movement and cracking through the plasterboard joints.
It can also potentially create a route for smoke through the wall construction.
Don’t simply see a piece of timber or plywood and think:
“That’s something solid to screw into.”
Look at how it is actually connected to the structural stud construction.
The fixing needs to be properly supported by the wall construction.
Check Masonry Carefully
Brickwork doesn’t automatically mean that everything is sound.
Check the opening for movement and inspect the masonry around your proposed fixing positions.
If the brickwork is damaged, loose or deteriorated, deal with that before relying on it to hold the frame.
When fixing into brick, don’t drill directly into the mortar joint.
I try to keep the fixing approximately 20 mm in from the edge of the brick where the construction and manufacturer’s fixing arrangement allow it, helping to reduce the risk of breaking out the edge and losing the fixing.
The actual fixing locations and fixing method must still follow the doorset manufacturer’s requirements.
Don’t Assume the Opening Is Just a Hole
This becomes particularly important in older buildings.
Some old openings have been made to work with whatever materials were available at the time.
I’ve found:
- pieces of timber being used as packers
- unusual old fixing arrangements
- voids hidden behind plaster
- paper pushed into gaps
- foam used to hold frames in position
- oversized architraves hiding previous work.
In some old buildings, the construction around the opening can be contributing to the stability of the brickwork above it.
Don’t start removing structural material simply to make the new doorset fit.
If removing the old frame exposes a structural problem, appropriate remedial structural work needs to be established before the new doorset is installed.
Look Behind Oversized Architraves
Oversized architraves can sometimes tell you that someone has been hiding a problem.
The same applies to unusually large skirting or other finishes around the opening.
If something looks excessive, ask yourself why.
I’ve seen situations where plaster has been used to disguise large voids.
I’ve also seen paper or other material pushed into a void and then covered over to make it look like a wall.
A finished surface doesn’t prove what’s behind it.
If you uncover a void, don’t simply cover it again with the new architrave.
If You Expose a Void, Deal With It
This is something that has never sat particularly comfortably with me.
I’ve removed old architraves and found little or no obvious fire stopping between the frame and the surrounding structure.
The attitude can sometimes be:
“If I can’t see it, I don’t know about it.”
But when you’re replacing the doorset and you’ve actually exposed the junction, I don’t think you should simply hide the problem again.
The fire doesn’t know whether you can see the gap.
If a void or inadequate frame-to-wall junction is exposed, it needs to be properly addressed before the architrave is replaced.
The fire-stopping method needs to be appropriate for the particular doorset, wall construction and permitted tested arrangement.
Falcon’s documentation gives specific tested frame-to-structural-opening sealing arrangements, including different wall types, materials and permitted gap ranges.
Don’t invent your own fire-rated construction because you’ve got a large gap.
Make Sure the Wall Is Actually Fire Resisting
This is one of the checks I think gets missed far too often.
I’ve arrived at sites to change fire doors and found an MF ceiling above the doorway.
You lift a ceiling tile and discover that the wall finishes just above the ceiling grid.
So what are you actually fixing the fire door into?
A fire door isn’t a magic solution that turns a non-fire-resisting wall into a fire-resisting wall.
A fire door is effectively a movable part of the fire-resisting construction.
The surrounding wall has to be capable of doing its job too.
If the wall isn’t actually fire resisting, or if there is a major void above the ceiling, that needs to be addressed rather than simply fitting the new doorset and assuming the problem has been solved.
Check the Structural Opening Hasn’t Been Compromised
Any work carried out to prepare the opening must not compromise the integrity of the fire-resisting wall.
This is particularly important in older buildings where the opening and surrounding construction may have been altered repeatedly over the years.
You might have to repair or reinstate sections of the wall before the doorset goes in.
If structural or fire-resisting construction needs to be reinstated, the appropriate construction and materials need to be established for that wall and application.
Don’t treat the structural opening as something you can simply cut apart until the doorset fits.
Check the Frame Depth Against the Wall
Sometimes the wall is simply deeper than the frame you can get manufactured.
This is particularly common with thick old brick walls.
That’s where a lining arrangement may be required.
The lining allows the frame arrangement to accommodate the additional wall depth and allows the finished architrave to reach the wall edge.
Without the correct arrangement, you can end up with the frame sitting too far into the reveal.
You may then be tempted to:
- leave one side of the frame deep in the reveal
- add a piece of quadrant
- push the frame further into the opening
- alter the architrave excessively.
These solutions can affect the finished appearance and, depending on how the frame is positioned, can even interfere with door operation.
The important thing is that any lining arrangement must be compatible with the specific tested/manufacturer’s doorset construction.
Check the Plasterboard Is Not In Your Way
On stud walls, check the plasterboard around the opening before putting the frame in.
If the board has been left projecting beyond the metal stud, it can physically prevent the frame from entering the opening correctly.
This is another reason I like to check the opening before I’m committed to fitting the frame.
If you don’t deal with it beforehand, you can find yourself trying to force a frame into an opening that isn’t actually clear.
Trim back what needs to be dealt with so the frame can sit correctly against the structure.
The First Real Test — Put the Frame In
Once I’ve checked the opening, I don’t want to spend ages making assumptions about what the frame is going to do.
I throw the frame in the opening.
It’s the thing that’s going to be fitted after all.
Why not use it to tell you what the opening is actually doing?
The first thing I look at is the head of the frame.
Is it level?
That gives me another indication of what’s happening with the floor and the opening.
If it isn’t where I expect it to be, I can then work out whether I need to:
- alter the frame height,
- make more room at the head,
- deal with the floor,
- break out an obstruction,
- or make another adjustment to the opening.
This is a first check, not an instruction to force or distort the frame.
You’re simply using the actual component you’re about to install to confirm what your measurements have told you.
🟧 Professional Tip
Sometimes the quickest way to find out what you’ve really got is to put the frame in the hole.
You’ve measured it.
You’ve checked it.
You’ve looked at the wall.
Now put the thing you’re actually fitting into the opening and see what happens.
It can immediately show you things that measurements alone don’t always reveal.
Don’t Forget What You’re Actually Fixing Into
By this point I want to know:
What is the wall?
Where are my fixings going?
Is the opening stable?
Is the opening square and plumb enough for the installation?
Is the wall actually fire resisting?
Is the frame the correct size and depth?
Is the floor going to work?
Is the frame-to-wall junction going to be correctly addressed?
If I can’t answer those questions, I’m not ready to install the doorset.
Key Takeaways
- Measure the opening at the top, middle and bottom.
- Take additional measurements wherever the opening changes.
- Measure the wall depth, not just the opening width and height.
- Check whether the wall is straight, level, plumb and square.
- Don’t assume an old plastered wall is consistent.
- Check the floor carefully, particularly in older buildings.
- Establish the finished floor level and manufacturer’s required undercut before installation.
- Check for obstructions around the door swing.
- Check where the frame fixings will actually land.
- Check metal stud and timber stud construction for movement and adequate reinforcement.
- Don’t assume visible plywood or timber automatically provides a suitable fixing.
- Check masonry before fixing into it.
- Avoid fixing into mortar joints.
- Avoid drilling too close to the edge of masonry where the fixing arrangement allows.
- Look behind oversized architraves and other finishes for concealed problems.
- Be alert for hidden voids and poor previous work.
- Don’t compromise the integrity of the fire-resisting wall while preparing the opening.
- If you expose an inadequate frame-to-wall junction, don’t simply hide it behind the architrave.
- Use the appropriate tested/manufacturer’s fire-stopping arrangement.
- Check that the surrounding wall is actually fire resisting.
- Consider linings where the wall is deeper than the available frame, using the appropriate doorset arrangement.
- Make sure plasterboard isn’t obstructing the frame.
- Offer the actual frame into the opening as an initial physical check.
- Don’t force the frame to compensate for a fundamentally unsuitable opening.
What’s Next?
Part 5 — Installing the Fire Door Frame
The opening has been checked.
The structure has been inspected.
The floor has been considered.
The fixing positions have been established.
Now it’s time to install the new frame.
This is where accuracy really starts to matter.
We’ll look at getting the frame into position, setting it correctly, securing it without distorting it, and making sure the installation starts from a sound and accurate reference point.
Part 4 – Checking the Opening Before Installation
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