You have three quotes on the kitchen table. Three builders who visited your house, measured the space, looked at the drawings, and sent back a price. One is forty two thousand. One is fifty one thousand. One is fifty seven thousand.
Most homeowners searching builders near me for their extension project pick the cheapest quote or the middle one and move on. They compare the total at the bottom of each page. They don’t read the details above. And the detail is where the problems hide.
Here are five red flags in builder quotes that most homeowners miss completely. Each one is a future invoice disguised as a missing line item.
Red Flag One: The One Page Quote
A rear extension involves foundations, drainage, structural steelwork, brickwork, roofing, insulation, windows, doors, electrics, plumbing, plastering, and decoration. Dozens of elements. Hundreds of individual materials and labour items.
A one page quote covering all of this is not a quote. It’s a guess with a number at the bottom. There is not enough space on one page to specify what is included in each element. Which means there is no way to verify what is excluded.
A proper quote for a forty to sixty thousand project should be three to six pages. Each element broke down. Each specification stated. Each allowance is clearly described. If the quote fits on one page, the detail fits nowhere. And the missing detail becomes your problem during the build.
Red Flag Two: Provisional Sums
A provisional sum is a placeholder. An estimate within the quote for an element the builder hasn’t priced accurately. “Provisional sum for foundations: two thousand.” “Provisional sum for drainage: fifteen hundred.”
Provisional sums get adjusted during the build based on actual costs. If the foundations cost three thousand instead of the two thousand provisional, you pay the difference. The quote said two thousand. The reality said three. A thousand pounds of surprise.
Every provisional sum is a potential variation. The more provisional sums in a quote the less the final bill will resemble the quoted price. Three provisional sums on a typical extension quote can add five to eight thousand to the final bill.
Ask the builder to convert every provisional sum into a fixed price. If they cant because they dont have enough information from the drawings, you need better drawings. Not more provisional sums.
Red Flag Three: Missing Drainage
Drainage connection is one of the most commonly excluded items in builder quotes. Connecting the new extension to the existing drainage system. Running new pipes. Installing new manholes. Connecting to the public sewer.
This work costs two to five thousand depending on the complexity. If it is not in the quote it appears as a variation in week two or three of the build. By then the builder is on site. You have no leverage. You pay whatever they ask because the alternative is an extension with no drainage.
Check every quote specifically for drainage. Is it mentioned. Is it priced as a fixed sum or a provisional. Does it include connection to the existing system or just the pipework within the extension footprint.
Your architect should have designed the drainage layout from Thames Water records. The builder should price this design. If the design doesn’t exist, ask your architect to produce it before you send drawings to any builder. A structural engineers near me search often leads homeowners to the technical professionals who coordinate with architects on exactly these details. Foundation design, structural calculations, and drainage layouts all need to be resolved before the builder quotes.
Red Flag Four: Scaffolding Without Duration
Most quotes say “scaffolding included.” Great. But included for how long.
A typical extension takes twelve to fourteen weeks on site. Scaffold rental is charged weekly. If the quote includes scaffolding for eight weeks and the build takes twelve, the additional four weeks appear as an extra. Roughly two hundred per week. Eight hundred in surprise scaffold charges.
Ask specifically how many weeks of scaffold are included. If the number is less than the quoted build programme, ask why. The scaffolding should cover the full construction period. Not an optimistic estimate of how quickly the builder hopes to finish.
Red Flag Five: No Making Good Allowance
Your builder will destroy your garden. This is not a criticism. Its physics. Excavation generates spoil that gets piled on the lawn. Materials are stored on the patio. The wheelbarrow route churns up the grass. The mixer sits where the flower bed used to be.
After the build the garden needs reinstating. New turf. Repaired patio. Replaced fence panels damaged during construction. This costs one to three thousand depending on the garden size and the level of damage.
Some quotes include a making good allowance. Many don’t. The ones that don’t are cheaper on paper and more expensive in reality. Because the garden work needs doing regardless of whether its in the quote. You either pay the builder or you pay a landscaper. Either way you pay.
How to Read a Quote Properly
Don’t start at the bottom. Start at the top. Read every line. Check every element against your architects drawings. Is the foundation depth stated. Is the steel beam specified by size. Is the insulation named by product. Is the drainage included with a fixed price. Is the scaffolding duration stated. Is the making good allowance listed.
Then check the exclusions. Every honest quote lists what is not included. Read this section carefully. If the exclusions list is long the headline price is artificially low.
Better still, ask your architect to review every quote before you sign anything. Fifteen minutes per quote. The most valuable forty five minutes of the entire project. They know what the drawings specify. They can spot whats missing. They identify the red flags before they become invoices.
Six to eight months from first conversation to completion. Five red flags. Five future invoices. All preventable by reading the quote properly before signing it.
