I can address the design/build side. Generally a design/build firm is an organization that is a licensed general contractor that concentrates in residential new construction and/or remodeling.

The design side of the business address the space design for the project. It is not interior design (not like what furniture, rug, drapes or pillows) but rather the plans for the space, location of elements, sizing, etc. During the design phase, a design/build organization will generally assist the client in selecting the materials and finishes to be used/installed during construction - cabinetry, flooring, molding styles, windows/doors, tile, countertops, hardware, etc. A design/build company may have an architect or plan designer (used to be called a draftsman) on staff, or they may accomplish the design phase by having a closely aligned group of professionals that participate on the project with them. To the customer it should be seamless whether they are on staff or an independent team brought together by the contractor.

There are several benefits of a design/build firm:

• The plans/blueprints generated are typically far more comprehensive and detailed
• Many of the issues of construction have already been identified and addressed by the time the plans are complete
• On the remodel side, issues and challenges of the existing structure will have already been identified prior to construction by the team that will be addressing it during construction. No loss of or misunderstanding of information because of handoffs from one company to another.
• The build side of the firm participates in design so there is more information up front regarding cost to build. There are no rude surprises after you pay for a full set of plans only to obtain bids and find the cost to build is 3x your budget.
• Many design/build firms operate in 3-D so that you have a very good understanding of what your space looks like and how all the parts come together.

I try and explain the differences in this simple manner:

Architect-bid vs Design-Build vs Build-Design

For me as a decades long design builder, the
group that is going to execute the design and be involved with the
client the most is the most critical.

Architect-Bid often assumes the critical differentiator between
builder/remodeler is price. They also often assume that the client
needs protection from the (implied) dishonest contractor. I submit that
if there is a lack of trust, the client and the contractor shouldn’t be
working together.

Build-Design – Buying the cheap (and/or inexperienced) design build
firm often results in “build-design” – poorly planned and reactionary
construction that can end up as a series of patches rather than a
well-conceived and executed design and project

Design-Build – for me, marries both the worlds (design and
construction). This requires a mutually respected team of a designer; a
builder; and an owner. The team is fairly paid for their expertise and
work and the client’s budget, wants and needs all get respected.
Win-win-win!