START HERE
Is the upstand staying?
That single question decides whether this is a half-hour job or a roofing job. Answer it before anything else.
Kingspan upstand, sound
DOME ONLY
The kerb stays, the unit comes off and a new one goes on. No roofing work, no membrane disturbed.
- Find the article number on the upstand label
- Confirm the internal opening still matches
- Check the flange and fixing points are undamaged
Use it when the kerb is Kingspan, in good order, and the roof around it is sound.
Someone else's upstand
SEND MEASUREMENTS
Often workable. Kerbs vary in internal opening and flange width, so this is a check rather than an assumption.
- Internal opening at the top of the kerb, both directions
- Flange width and upstand height
- A photograph with a tape measure in shot
Use it when you did not supply the original and there is no label.
Send it overUpstand coming out too
DOME + UPSTAND
If the kerb has failed, or the roof is being re-covered, both parts are replaced and the build-up may have changed.
- New build-up depth means a new upstand height
- Roofing contractor needs to be in the conversation
- Order both together so they match
Use it when the kerb is damaged, rotten, or the roof is being re-covered.
Choosing an upstandWHAT HAVE YOU GOT
Identifying the existing unit
You need one of three things, in order of how much time they save.
In order of preference
- 1 The article number, from the label on the upstand or the unit. With this we can match it exactly in one message.
- 2 The original order or invoice, if it came from us. Same result.
- 3 The measurements. Internal opening at the top of the kerb, both directions, plus the upstand height and flange width. This works even when every label has gone.
DIAGNOSIS
Why domes fail
Worth knowing which one you have, because two of these mean the unit is the problem and two mean it is not.
| What you are seeing | Usually means |
|---|---|
| Crazing, cracking or brittleness | Age and UV. The unit is at end of life |
| Discolouration or yellowing | Age. Light transmission will have dropped with it |
| Condensation between the shells | A failed seal. The unit is the problem |
| Condensation on the inside face | Often the room, not the unit — ventilation and humidity |
| Water tracking in at the edge | Usually the flashing or the membrane, not the rooflight |
| A cracked or distorted frame | Impact, or movement in the structure below |
| The opener no longer holds | The actuator, which can often be replaced on its own |
If it is the last two rows, replacing the dome may not fix anything. Send a photograph before ordering.
WHILE YOU ARE UP THERE
Check these at the same time
Access is the expensive part of a rooflight replacement. If there is scaffolding or a hoist on site, the marginal cost of dealing with everything at once is small, and the cost of going back up in eighteen months is not.
- The other units on the same roof. They are the same age and were fitted on the same day. If one has failed, the others are on the same clock.
- The upstand itself — corrosion on steel, splits or distortion in PVC, and whether the fixings still hold.
- The flashing and the membrane termination. Most water coming in near a rooflight is coming in at this junction rather than through the unit.
- The opening gear, if the unit ventilates. Actuators are often replaceable separately.
- Whether the specification has moved on. A unit fitted twenty years ago will not meet what would be specified today, and a like-for-like replacement locks that in for another twenty.
WORTH ASKING
Like for like, or better?
A replacement is the cheapest opportunity you will ever get to improve the opening, because the access is already paid for and the opening is already there.
Three upgrades are worth pricing at the same time as the like-for-like: a higher-performance glazing build-up where the thermal figures matter; Opal instead of Clear where glare over a workspace has been a complaint; and ventilation where the room has none and the opening is the obvious place to put it.
None of these are automatically the right answer. But they cost almost nothing extra to ask about at quote stage, and a great deal to add later.
QUESTIONS
Common questions
The label has gone. Can you still identify it?
Usually. Send the internal opening at the top of the kerb, both directions, the upstand height and flange width, and photographs of the unit from above and below. That is normally enough to identify what will fit, even when the original is unidentifiable.
Can I get exactly the same unit again?
If it is a current line, yes. If it is old, the equivalent in the current range will fit the same opening but may differ in glazing or detail. We will tell you what has changed rather than sending a substitute and hoping.
Do I need scaffolding?
That is a decision for whoever is doing the work, based on the roof and the access. It is not something we can advise on from a product page — but it is worth settling before you order, because it usually costs more than the rooflight.
Several units on one roof — do they all have to match?
Not technically, but they will look mismatched from below and inside if the glazing differs. If you are replacing some now and some later, order the same specification both times, and tell us so we can note it against the account.
How long does the actual swap take?
Where the upstand stays and the unit is a straight replacement, it is a short job. Where the kerb comes out, the membrane is disturbed and it becomes roofing work with a drying and dressing sequence. Which is exactly why the first question on this page is the one that matters.
Photograph it and send it.
The upstand label if there is one, the internal opening measurements if there is not, and a shot of the unit from below. Most replacements are identified from that alone.
Guidance on this page is general. Decisions about access, working at height and the condition of the roof are for the contractor carrying out the work.