Material costs in residential renovation fall into a few distinct categories, and they behave differently from each other. Treating all materials the same way — either by defaulting to the cheapest option everywhere or by spending heavily on everything — is a good way to end up with a project that's either technically adequate but unpleasant, or beautiful but poorly built beneath the surface.
Structural and functional materials
This includes anything that you won't see once the project is finished but that determines how the building performs: insulation, pipe fittings, electrical cable, floor joists, damp-proof membranes. These are areas where cutting to the minimum specification has real consequences over time, and where the difference in cost between a standard and better product is often small relative to the total project budget.
Contractors frequently use the cheapest products in these categories because homeowners can't see them and don't know to ask. This is one of the things a material specification in a scope document addresses: naming minimum standards for the elements that aren't visible.
Finish materials where specification matters
Floor tiles, bathroom fittings, kitchen fronts, door hardware. Here the cost variation is significant and the quality difference is real — but the quality you need depends on context. A floor tile in a high-traffic entrance hall needs different characteristics than the same tile in a guest bedroom. A bathroom tap used daily by three people will behave differently over five years than one used occasionally.
The questions worth asking before specifying finish materials are functional ones: how often, by how many people, in what conditions. The answers determine where quality genuinely matters and where spending more buys something real versus just a higher price point.
Where contractor markup is standard
Most contractors add a margin to materials they supply — typically somewhere between 15% and 35%, sometimes higher for specialist items. This is standard practice and not inherently unreasonable: sourcing, managing delivery, and holding responsibility for the right material arriving on site has a cost.
The question is whether the markup is disclosed and whether you have the option to supply materials yourself. In some cases — particularly for expensive finish items like tiles, kitchen units, or sanitary ware — procuring those items directly can produce meaningful savings. The contractor installs what you supply; you've paid retail but avoided the markup.
The risk in supplying your own materials is that the contractor typically won't be responsible for defects or shortfalls in what you've provided. If the tiles arrive damaged, that's your problem to resolve. This is a trade-off worth understanding before you decide.
Lead times
One of the least-discussed aspects of material costs is lead time. A material that arrives on schedule has a different effective cost than an identical product that causes the project to pause for three weeks while it's sourced. That delay has a cost — in extended rental, in contractor rebooking fees, in the friction of getting a project back on track.
During the design phase of a project, it's worth asking about lead times for any non-standard item before you commit to it. "Lead time of 6–8 weeks from Belgium" means the material needs to be ordered before work starts, not when it's needed on site.