Using the Detail Library: Live Project Case Study

An introduction to the case study project

The case study project is a new two storey, detached, single dwelling for a private Client. The project is generally clad in rendered blockwork with some feature stone details and a pitched slate roof. There are also smaller areas of timber cladding and areas of flat roof.

To allow a swift start on site following planning consent, the design team and the Contractor have started coordinating the detailed designs for the external envelope of the building. Collaboration between the Contractor, the Client and the design team has helped to direct the detailing process from the outset.

The involvement of the Contractor at the design stage has a significant influence on the developing detailed design of the project. The Contractors preferred methods of construction can be reviewed and accounted for during the design stage. It also allows the design team to have access to the contractors preferred subcontractors, who can provide their expertise to the project at an earlier stage. In projects where the Contractor isn’t on board at the initial detailing stage, the process is much the same but the design decisions are made by the team without the Contractor (who may or may not have different ideas when they come on board).

The key drivers informing the detailed design

There are several factors which drive the detailed design process. Some projects may have a strict set of project specific criteria that the construction needs to achieve.

For example, the Client or Contractor may have a particular construction method that they would like to use, the Client may have a specific aesthetic that they need to achieve or the site may have certain constraints that favour one method of construction over another. Other projects may have fewer project specific requirements and are more driven by the local regulations.

Below are some of the many factors which may influence the development of construction details for a project:

• • • Building regulations requirements – including stopping the spread of fire, providing acoustic performance, means of escape, accessibility, energy efficiency, sufficient ventilation, protection from moisture and contaminants, structural support, security, preventing overheating and servicing the building.
    • Planning requirements – planning restrictions imposed on the project or conditions of the consent. These may include approval of the external materials or approval of the Contractors construction method etc. Some projects may also require the approval of critical aesthetic details such as window reveal details.
    • Site specific requirements – the site may have particular constraints such as particularly challenging ground conditions, topography, exposure to weather, the need to protect existing site features during the build, access limitations, working area restrictions etc.
    • Client driven project specific requirements – there are numerous enhancements that the Client may require e.g improved energy efficiency, life cycle assessment considerations, improved acoustic requirements, improved security, improved fire protection etc. The Client may also have particular products or suppliers that they would like to use on the project.
    • Contractor driven project specific requirements – if the contractor is on board at the design stage, they will likely have preferred construction methods and subcontractors based on their previous experience.
    • Design team driven project specific requirements – members of the design team may have particular specialities, experience or insurance limitations that will drive the design in one direction or another 
    • Structural warranty requirements – the Client may require a specific third party warranty. The warranty provider will have their own technical standards which need to be met at each stage of the construction.
    • Project budget – the complexity of the details, construction methods and selection of materials can all have a significant impact on the cost of the project. It is important to develop details that provide the best value for the Client in line with their budget.
    • Project timescales – the timescale available to complete the project may rule out some construction methods or design solutions and favour others.
    • Availability of materials and labour – readily available materials and labour are likely to influence the choice of construction and development of the details. Specialist labour and tools may increase efficiency or improve quality when they are available.

The requirements for each project will be unique and some will have more defined requirements than others. The sooner any requirements can be agreed the better as this will allow them to be considered from the outset and avoid rework later in the construction process.

Identifying relevant details to download from the Detail Library

Reasons to be mindful of construction at an early stage

Fixing the external building perimeter at planning stage

Using the Detail Library to help inform initial envelope thicknesses

On the case study project, site assembled timber frame construction is the Contractors preferred construction method due to access limitations (a narrow single track road) and their recent experience on other projects.

There are a vast number of construction details within the Detail Library and these include numerous timber frame details. A quick search of the Library allowed similar details to be identified and downloaded for reference.

The narrow single track access road to the site

This image shows a section view extract of the approximate thicknesses for walls, floors and roofs used at the planning stage and the relevant Detail Library details which were useful in informing these initial values.

Approximate thickness 3 referencing Detail Library detail TR5 (timber pitched roof)

The more realistic the envelope thicknesses can be drawn at the early stages of the project the better as it will help to avoid more significant changes or design issues later in the design process. However, it is still important to allow for flexibility in the design and assume that the thicknesses will change during the detailed design process. Change is almost always inevitable as more requirements are introduced and typical construction build ups are developed into project specific details through collaboration with the design team, contractor, subcontractors and manufacturers.

Starting the detailed design process for the building envelope

To start the detailing process, it can be useful to identify the project specific details which are vital to the construction of the building envelope. There may be several different wall, roof and floor build ups within the project and a greater number of different junction details between them. There may be several opening types (such as windows, doors and rooflights) which will each interface with the envelope too.

At the start of the detailed design process, a set of planning stage building sections for the case study project were marked up to identify key details and the thermal performance requirements of each building element. As each detail was considered, further requirements were assigned to the building elements, such as fire performance and acoustic performance. The number of different performance criteria for each element of a project will be dependent on the regulation requirements and any project specific requirements that have been identified.

Once the requirements of any critical build ups and junction details have been identified, these can begin to be translated into a set of working details. Developing the details will require coordination with the design team, the Contractor (if appointed), subcontractors and product manufacturers.

An example detail developed using the Detail Library

The following example shows the progression of a section detail for a ground floor to external wall junction within the case study project. The section view is taken through the external wall of a utility room on the ground floor and also shows the position of a window cill above a worktop. At this stage, only the approximate thickness of the wall and floor are shown and their key performance requirements are noted. The external wall is to be timber frame with a rendered blockwork outer leaf and the ground floor is to be of a beam and block construction.

A search of the Detail Library reveals a number of details which will assist in the creation of the junction detail.

Detail Library detail TG4 shows the junction between a timber frame wall and a beam and block floor. Detail Library detail TW8 shows the junction between a timber frame wall and a window cill.

These details were downloaded and used as a starting point for the creation of the project specific junction detail to save a great deal of time and effort (compared to starting the detail from scratch).

Firstly, the standard details were manipulated to align with the project specific view by changing their orientation. Next, some tweaks were made to the detail to suit the project specific requirements.

The amendments were coordinated with the wider design team as follows:

• The structural arrangement and dimensions of the timber frame, beam and block floor, foundation and window support were tweaked to suit the structural engineers design
• The brick outer leaf was updated to blockwork with a render finish to suit the project aesthetics. The depth and detailing of the render was coordinated with the preferred render manufacturers details
• The insulation was updated to suit the specific products chosen to be used on the project. These were coordinated with the Contractor and chosen insulation manufacturers. U-value calculations and condensation risk calculations were obtained from the insulation manufacturers to prove the specifications would meet the required performance.
• A service cavity was added internally to the depth requested by the Contractor
• The floor screed thickness and relationship to the floor membranes / insulation was checked to ensure that it met the requirements of the chosen underfloor heating system
• The addition of a decorative stone plinth and window cill was coordinated with the chosen cast stone manufacturer
• The internal plasterboard lining was reviewed with the plasterboard manufacturer to check that the external wall build up would meet the project’s fire resistance requirement
• The window frame depth was coordinated with the chosen window manufacturer and the window alignment tweaked to suit the project aesthetic

The case study project is modelled in Revit and so the Revit files in the Detail Library were used in this example. AutoCAD files and Sketchup files are available too and can be tweaked in the same way to suit project requirements!

Be prepared for design development!

As projects progress, there may be changes needed to the details for various reasons. Following the initial draft of the technical details for the case study project, it was decided that a raft foundation would be more efficient than a beam and block floor with strip foundations. Using further Detail Library details as a starting point, the project details were quickly updated to suit the new arrangement shown below.

Detail Library detail TG4

Detail Library detail TG3

Conclusion and future updates

This post has looked to briefly illustrate how the details within the Detail Library are being used to help progress the detailed design of a case study project. Several Detail Library details are being used in combination to provide a key starting point for the development of project specific details. This allows a great deal of time to be saved during the initial drafting stage. The Detail Library resources are used in combination with the expertise of the design team, Contractor and manufacturers to develop a robust set of details for the project.

As the case study project progresses, we hope to look in more detail at how the Detail Library details are being used to develop key junction details. We will also consider how the different elements of the building regulations define the project specific requirements for each building element. Keep an eye out for future updates.

All of the standard details featured in this post can be downloaded from the Detail Library. For details follow the links below.

Download the Details

Links and Image Credits

Source URL: https://www.selfbuildanddesign.com/beginnersguides/nextsteps/timber_frame

Image URL: https://www.selfbuildanddesign.com/editorial_images/page_images/featured_images/materials/a_fast_quality_build.jpg

Architect credit: Unknown

Photographer credit: Unknown