Sliding doors supply and fit, and what the scope should actually say

What sliding doors supply and fit should include, line by line

When you ask for sliding doors supply and fit, you are asking one company to take responsibility for the whole chain: measuring, making, delivering, lifting, installing, sealing, certifying and guaranteeing. The value is not that it is convenient. The value is that there is one organisation to blame, which matters enormously on a product where a 3mm error at survey becomes a remake with a six week lead time.

A scope worth signing should name all of this explicitly.

• The survey, stating who takes the dimensions and therefore who owns them.
• Manufacture, with the system named by series, frame colour and finish specified, and glass make-up written out in full.
• Delivery and offload, including who provides the vehicle and who is responsible for the glass from the kerb inwards.
• Lifting: the method, the equipment, and whether craneage or mechanical lifting is included or excluded.
• Removal and disposal of the existing doors and glass, and whether a skip or waste transfer is included.
• Checks on the structural opening before manufacture, including the permitted deflection of the structure above.
• Installation: fixings, packing, levelling, threshold bedding and connection to the external drainage.
• External sealing and weathering of the perimeter.
• Commissioning: panels hung, rollers or carriages adjusted, locks aligned, seals checked, and a demonstration to you.
• Certification and paperwork, with the route stated.
• Making good, with its scope written down and its exclusions named.
• Payment stages, lead time and the guarantee terms for frame, glass, hardware and installation separately.

Anything not on that list is outside the price. That is the whole point of writing it down.

Supply only: what you are taking on

Supply only is cheaper, and sometimes it is right. What you are buying is frames, panels and glass delivered to site. What you are accepting is every other risk on the list above.

You own the dimensions, so a remake is yours. You own the lifting, which on a large panel means hiring equipment and finding competent people. You own damage from the moment the glass is offloaded, and an aluminium frame with a knock in the powder coat on a visible face is a remake, not a touch-up. You own storage, which for sealed units means upright, dry, out of direct sun and off the ground. You own the fit tolerance, the packing, the levelling, the sealing and the drainage connection. And you own certification, which means a building control application rather than an installer’s certificate.

Supply only makes sense when there is a competent main contractor on site who will take the sizes, carry the risk and do the work, and when the programme needs the frames early so the building can be made weathertight. It rarely makes sense for a homeowner with a capable friend and a van. The saving against a sliding doors supply and fit price is a modest percentage of the job, and one broken panel or one remake wipes it out several times over.

Who is liable if the opening is the wrong size?

This is the question that decides most arguments on sliding door jobs, and it has a simple rule behind it. Whoever measures owns the size.

On supply and fit we survey, so it is ours. That is why we will not manufacture from somebody else’s drawing or a dimension read down the phone unless the client accepts in writing that the sizes are theirs. It sounds unhelpful at the point of asking. It is the only honest position, because an aluminium sliding door is made to the millimetre for one opening and cannot be adjusted on site like a timber frame.

On supply only from a builder’s dimensions, the builder owns it. Make sure the builder knows that, in writing, before he gives you the numbers, because builders who have never ordered a sliding door sometimes measure a brick opening and forget the plaster, the screed and the tolerance the frame needs.

One thing to challenge directly: if a company offers you supply and fit but takes your own measurements rather than surveying, ask who pays for a remake if the opening and the door do not agree. If the answer is anything other than them, that is supply only with an installation service bolted on, and it should be priced as such.

Lifting, craneage and access are a cost line, not an afterthought

On a large sliding door, getting the glass to the opening can be a meaningful share of the cost of the job. The options are a carry with suction lifters, a tracked glass manipulator, a scaffold tower, a genie lift, a hiab or a spider crane over a roof, and in central London occasionally an out-of-hours lift because the street cannot be blocked in the daytime. Add a parking bay suspension with several working days’ notice, a licence where a crane sits on the highway, and permission from building management if you are in a mansion block.

What matters commercially is who hires it, who pays if a visit is wasted, and what happens to standing time. If a crane is booked and the street is blocked by somebody else’s skip, somebody pays. Settle that before the day, not during it.

And challenge the phrase if required. A quotation that lists craneage or mechanical lifting as if required has not assessed your access, which means the price in front of you is provisional whatever it says at the bottom. Either the assessment has been done and the cost is in, or it has not been done and you do not have a fixed price.

Making good, and the gap between a glazier and a plasterer

On a replacement, removing the old frame always disturbs the internal finishes. On a new opening, the frame goes in before the plastering and the flooring. Those are completely different handovers, and the scope needs to say which one you are buying.

Our line is drawn in the same place on both. We leave the opening structurally sound, weathertight, sealed externally, with the threshold bedded and drained, and we take the old doors away. Plastering, tiling, flooring, external render and decoration sit with your builder or decorator unless we have specifically priced otherwise. We say which trades you still need, at survey, rather than after the event.

The failure mode to avoid is a builder who plasters and tiles up to an opening before the door arrives. Then the frame goes in and every one of those finishes gets cut. Sequence beats scope here.

Sequencing with your builder

On a new opening or an extension, the right order looks like this. Structure in and cured, with the beam sized to meet the glazing system’s deflection limit, not just its own strength criterion. Deflection head detail agreed. Cavity closers and damp proof course in place at the jambs and head. The opening formed to the surveyed dimensions and within the tolerance we have given, which is a tighter tolerance than most brickwork is built to.

Then the floor build-up has to be known before the threshold level is set, because screed and finish depths decide whether the threshold lands flush, and nobody can unwind that decision afterwards. Frames in early enough to make the building weathertight, glass in once the worst of the wet trades are done, threshold protected while other trades work over it, and final adjustment after the floor is laid, because a floor laid against a threshold can change how a panel runs.

Sliding doors do not like being installed into a programme that has not thought about them. The frames need the opening right, and the opening is built weeks earlier by someone who may never have seen the door drawing. Getting our survey dimensions and tolerance into the builder’s hands early costs nothing and prevents the most expensive mistake on the job.

Certification: FENSA on a replacement, building control on a new opening

This confuses people and it is worth being precise. Replacing doors in an existing dwelling is notifiable work, and an installer registered with a competent person scheme such as FENSA can self-certify it and issue a certificate. We are FENSA registered, so on a replacement you get that certificate, and your solicitor will want it when you sell.

New openings, extensions and conversions are different. There the glazing is part of a wider set of works covered by a building control application, inspected and signed off as part of the project, and there is no separate FENSA certificate. If somebody promises you one on an extension, they have misunderstood the regime. What you should expect instead is the system data, the glass specification and the U-values your building control officer needs, and we provide those as a matter of course.

Where supply and fit quotes hide money

Provisional sums for anything. Craneage if required. Making good excluded with no statement of what that leaves you. Glass listed as to be confirmed. Hardware described as standard with no finish or series. Delivery and offload excluded, which quietly puts the risk of a damaged panel onto you. Parking, permits and bay suspensions charged at cost later. Waste removal extra. And a payment schedule weighted heavily to the front, which transfers risk from them to you for no benefit in return.

The test is simple. Read the quotation and ask what could arrive as an extra. If the answer is more than one or two clearly named contingencies, it is not a fixed price, and comparing it against a properly scoped quote on headline figure alone will mislead you.

How we price sliding doors supply and fit

Free survey across London before anything is ordered. A written fixed quotation naming the system and series, the configuration and handing, the clear opening in millimetres, the glass size and make-up per panel, the lifting method, the making good scope and the exclusions. Our own glass workshop in Wembley making the units, and our own installation teams fitting them.

We will also quote supply only where there is a competent contractor to receive it, with the measurement responsibility stated plainly on the order. If supply only is the sensible route for your job we will say so. If it is not, we will tell you that too, and explain which risk you would be taking on.