A question like that is common for home builders to hear from customers. It is not unusual for the client to request that a trade contractor that they have worked with in the past be used instead of those subcontracted by the builder. They may also ask to use specific brands or materials, such as carpeting or plumbing items. There is a good reason that the majority of builders do not agree to this. Standing by proven and familiar subcontractors is beneficial for both the client and the builder. The reason has to do with the relationships between the parties involved: The builder, the supplier and the subcontractor.
To begin with, we will talk about purchasing from suppliers. Most builders have a selection of approved suppliers for the sake of reliability and standardization. The warranty was created based on the performance of reliable materials that the builder is used to working with. If a builder allowed the client to choose unfamiliar products from an unproven vendor to fill critical roles in the home, that could put the guarantee behind the warranty at risk.
For instance, if the homeowner were to order a carpet from a supplier that was not approved by the builder, then discovered that it was from a European carpet supplier that takes many weeks for delivery and it is made with metric measurements. Products from unfamiliar suppliers bring an element of risk with them, potentially capable of putting the whole project behind schedule.
The reasons for using trusted contractors are even more evident. Most builders rely on subcontractors as much as their own workers. Trade partners are an essential part of the building team. As such, the builder will usually only give highly important jobs to subcontractors who have demonstrated skill and reliability. With familiar partners, it can be easier to give the homeowner an accurate estimate and stand behind the quality of the work.
To see whether a subcontractor will be a good fit for a larger project, they will usually hire them for smaller jobs and evaluate their performance over a period of time. They should be able to produce work of high quality, able to stand up to the requirement of the warranty, on a consistent basis, they should work well with the project managers, they should be able to make accurate bids, and they should be reliable and responsive. It might take years to determine a professional's skill level and build up trust to the point that they can be let loose on large, complicated projects with minimal supervision. A single good job does not necessarily guarantee that future jobs will be handled with the same level of quality.
If a builder allows the client to hire unproven subcontractors, they lose a measure of control over the project. An unfamiliar subcontractor can be a wild card. There is no way to know for sure how they will perform or how they will interact with the other workers on the project. And even if the homeowner agrees to be responsible for the final result, and potential problems could still reflect negatively on the reputation of the builder. And a good reputation is one of the most vital qualities of a successful home builder.
In the end, construction is an industry where good relationships are key. Maintaining amicable partnerships with trusted subcontractors is one of the primary assets to making a the construction process go smoothly. And the relationship goes both ways. If the subcontractor fulfills their end of the deal, they deserve to get paid a fair price and have their shot at the major contracts they have worked hard to earn.
Not everything will always go completely according to plan, and when problems arise, such as poor weather or delays in shipping, a good relationship with a subcontractor can pay off. If the builder and subcontractor have a mutual familiarity and respect, they might be more inclined to make adjustments in their schedule to make sure the project stays on track. Everyone's on the same team.