For many years, wood frame wall panels have been constructed on site by contractors, and, in more recent times, by component manufacturers too. The wall panels assembled by component manufacturers primarily are open panels. These consist of lumber studs at predefined centers sheathed externally with OSB or plywood inclusive of openings such as windows and doors. In some instances, the building paper will be factory fitted, but it wouldn’t be uncommon for this to be site fixed.
Open panel systems are an excellent alternative to site stick framing and are the most common choice for individuals and companies looking for a prefabricated solution. There is still, however, the requirement for further contractors to install additional elements, including insulation, vapor barrier, battens, services, and drywall. If project timescales are tight, then a closed panel system would be a fantastic option, because it can incorporate many of the constituents that make up the complete wall structure.
The benefits of closed wall panel systems include the following.
Speed of Install
As with open panel systems, the speed at which any prefabricated panels can be installed is very fast – especially when a crane is utilized. Due to the longer length of closed panels, this process is even faster than the open panel counterpart. (Reasons behind the preference for increased panel length will be discussed shortly.)
Reduced Site Waste
In addition to the reduced lumber waste you’d expect from prefabricated panels, any of the constituents included in the panel will offer the benefit of reduced site waste, and therefore costs inclusive of removal and disposal too.
The quality of workmanship and materials is subject to the component manufacturer’s quality assurance (QA) procedures and protocols. These QA procedures and protocols can run from the design office, through the factory, and to delivery and offload. It’s worthwhile checking what trade bodies the component manufacturer is affiliated with and if the material they use is FSC and PEFC certified.
Less On-Site Contractors
The closed panel system arriving on site allows for a single contact – the component manufacturer – instead of contacting many different contractors to schedule and carry out their relative trades. Another benefit of note is the dramatic reduction in timescales due to the reduction in site works required to complete the wall panels.
Certain Panel Performance
When performance is of great importance, high R values, low U values, and air tightness make a closed panel system an excellent choice. Factory fitted insulation, membranes, and window units will undergo the component manufacturer’s quality control checks, guaranteeing the building designer’s predefined value specifications.
Firm Cost Calculations
When looking at costs, closed panel systems can seem expensive initially, but this is only when comparing them to a relatively open panel system. The component manufacturer will be able to produce firm costs, and this is of great benefit if the project has a tight budget. A reduction in on-site contractor costs, material waste, and any unforeseen extra overs restricts the chances of running over budget.
The list of benefits could continue, but there are some challenges worth considering when deciding if this would be the right system for a prospective project.
Long Panel Lengths
Closed panel lengths of 30’+ are recommended; this is due to the desire to keep panel junctions to a minimum in relation to thermal and air tightness continuity. With panel lengths being 30’+, however, there can be challenges in regards to individual panel weights and maneuverability at the component plant and on site.
Alterations to 2nd Fix / Finish
It is extremely important that a design freeze is established prior to the closed panel system design being signed off for production. If an architect or building designer changes the location of an electrical socket, for example, this can cause additional remedial works and costs on site. Having spoken to a colleague, his company does not fit the drywall and sockets around the kitchen area for this exact reason, as it is a repeat problem area.
Closed wall panels are more rigid than their open panel counterparts. This is due to their included constituents, such as drywall or cement board. This becomes an issue in relation to internal panels that are not yet clad, causing different rates of expected settlement in the structure. It therefore would be advised that, in particular, the internal load bearing partitions are also pre-clad with drywall or cement board to increase their rigidity in line with the external walls.
Delivery to Site
It is important to consider the logistics of delivering the closed panels to site safely and undamaged. It is common practice here in the UK to deliver open panels laid horizontally stacked up. This is not possible for closed panels, however, due to the risk of damage to pre-fitted windows, doors, and drywall. Instead, it is recommended that closed panels are delivered in a vertical orientation. Another consideration, especially if you operate in a changeable climate, is moisture such as rain or snow. The panels should be wrapped to keep them weatherproofed for transit. This adds additional costs to consider.
Upon review of the benefits and potential challenges of utilizing a closed panel system, I feel that there are many worthy benefits and it is something that I’d be happy to offer prospective clients. It is true that not every project would be a suitable candidate, but, if speed to completion and tight budget constraints are significant factors, then a closed panel system may be the one to put forward. As I’ve mentioned, the initial cost of a closed panel system may seem high at first, but, when the bigger picture is examined, it remains competitive.
With 16 years in the roof truss and timber engineering industry, working in the UK, Europe, and North America, Greg Watson currently lives in Scotland and is the Design Manager at a Northern Irish component manufacturer. He has a passion for large and complex timber structures and seeks to promote timber as a sustainable building material.