Before the Walls Go Up: Planning Decisions That Shape a Custom Home
For most people, visualisation of their future home is dominated by aesthetics — the colour of paint, the type of stone on the bench tops, the style of the tapware. However, the real decisions that shape the ambiance of the home are made weeks before these items are selected. And they are all hidden away in a framing plan that only the builder and engineer will spend hours discussing. Wall thicknesses, stud sizes, ceiling heights, and bracing configurations all play a part in determining whether the home will be comfortable, cosy, and light-filled long after the final cushion has been placed on the couch.
Decide on wall depth first — it dictates everything else
The most important decision when choosing the stud size and centres is deciding on the cavity depth. Studs are commonly 90×35 or 140x45mm, with centres of either 450 or 600mm. You may think that this decision has little bearing on anything else, but it is, in fact, your largest lever for optimising the performance of the walls.
A 90mm stud provides a 90mm cavity for insulation, whereas a 140mm stud provides nearly double the depth for a much-needed boost to insulation capacity, especially in cold climates. Increasing the cavity depth also provides more room for acoustic insulation, which would otherwise be challenging to fit in a shallow cavity, limiting its capacity and effectiveness.
While reducing the stud centres from 600 to 450mm provides a stiffer frame, it also allows more fixing options for tiling and other heavy-duty linings. It uses more timber, however, and creates additional thermal bridges that reduce the effectiveness of insulation. The reduction in stud cavity depth also reduces the amount of cavity insulation that can be installed. Thermal bridging occurs when timber framing conducts heat from the inside to the outside faster than insulation can handle on its own, and it is an important consideration when comparing timber to steel framing, another popular alternative building material. Timber bridging is much less prevalent and should also be considered when choosing between frame materials.
While these considerations will have no bearing on your rendered plans, they will dictate whether your bedroom next to the street will be warm in winter.
A ceiling height is a framing decision, not a finishing one
Higher ceilings create the illusion of a larger home without adding more square metres. Increasing a ceiling height from 2.4 to 2.7 or 2.7 to 3.0m will create the illusion of a much larger room without spending a fortune on square metres.
However, increasing the ceiling height also increases the required bracing capacity for walls, as well as introducing new lintel requirements for openings. It also uses more timber, so, while it is not as expensive as it sounds, it will affect the final cost nonetheless. If choosing to increase the ceiling height in certain rooms only, make sure to talk to your builder about bracing capacity before committing to a framing plan. Changing the ceiling height after the fact is much more involved and may require complete reprofiling of certain areas to achieve the desired effect. Another consideration when choosing a ceiling height is the MGP rating of the timber. MGP10, MGP12, and MGP15 are all ratings of the load-bearing capacity of the timber. Higher ceiling heights and spans generally require higher MGP ratings for bracing capacity.
Asking your builder about the recommended MGP rating for both load-bearing and bracing walls is a sensible way to start asking the right questions about framing.
Bracing walls dictate the placement of windows
One of the most overlooked details when planning a home is the presence of bracing or shear walls. They are most often recommended by engineers when designing the framing plan in accordance with AS1684. Their primary function is to resist lateral and wind loads exerted on the structure.
The most important consideration when planning shear walls is that they cannot be replaced by large expanses of glass, unless specifically designed to do so. Shear walls are often positioned along longer walls, and their removal or replacement with glass will compromise the integrity of the structure. If large windows, or even bi-fold or stacker doors, are envisioned for a particular part of the house, the framing plan must be altered to accommodate these changes. This would most often take the form of removing bracing requirements for a particular wall, and redistributing them elsewhere in the plan.
Making these decisions on the fly often leads to either compromised design elements or expensive engineering solutions such as portal frames. Consulting openly with the designer and engineer about bracing requirements and possible design alterations is important, and should ideally occur before framing begins, while plans are still being discussed.
Large openings dictate the presence of lintels in the ceiling line
Bi-fold and stacker doors are all the rage these days, and for good reason — they help achieve that sought-after indoor-outdoor connection. However, large openings such as these require lintels or boxed headers above them to carry the load that would have been carried by the removed portion of the wall.
The larger the opening, the deeper the lintel needs to be. A deep lintel over a 4m span, for instance, will push the ceiling line down and back at the point of the opening, creating an uneven ceiling height inside. This effect can also be seen on the outside if the boxed header is not built out to meet the ceiling line. Another consideration when boxing a header is the services that may need to be routed above the opening. It becomes much harder to route services such as ducting or electrical cabling around an opening if the ceiling height has already been dictated.
When choosing the location of large openings, make sure to account for ceiling heights, especially if the opening is to be boxed. In cases of large openings, make sure that the lintels ordered are compatible with the ceiling line and not just the structural requirements of the building.
Decisions on frame material and species
Having chosen the dimensions, the decision on frame material is relatively simple — timber framing is, by far, the preferred choice in residential construction. There are several reasons why timber-framed buildings offer superior performance over their steel-framed counterparts. Timber is much easier to work with, which means faster installation and fewer errors on site. It also conducts heat much less readily than steel, helping to retain warmth in the building. Finally, timber is much less likely to introduce cold-bridging into the insulation continuum, while still being forgiving enough to allow for minor on-site inaccuracies while remaining code-compliant.
There are several reasons why timber is a great choice for residential framing, and the deciding factor may well be the cost. Timber is, in most cases, cheaper than steel, making it much more desirable in residential construction. Perhaps its most appealing quality, however, is the aforementioned reduction in cold bridging. A well-constructed timber frame will have fewer weak points in the insulation blanket, allowing for a much warmer and more energy-efficient building.
Two considerations that most people overlook with Timber Wall Frames are the species of timber used and the level of preservation. Both factors are integral to ensuring the longevity of the framing and should be chosen in accordance with local climate and design requirements rather than what is available at a local supplier. Choosing the appropriate level of H1.2, H2, or H3 treatment for framing timbers is much more important than it may seem at first. The wrong level of preservation can lead to rot or termite damage long after construction has been completed and hidden in the confines of a wall cavity.
Species choice is also important, particularly in architectural timbers such as Western Red Cedar. This type of timber is often used in exposed rafters, posts, and other features requiring a higher standard of visual appeal. When ordering structural timber framing, it is important to discuss both options with a supplier to ensure that the timber selected will match the design specifications. In most cases, it will be cheaper to utilise a lower-grade timber for structural applications, while upgrading to appearance-grade cedar for exposed features. It is important to budget accordingly, and to separate the two when ordering to prevent overspending on either.
Creating service cavities rather than notching stud walls
When planning the internal services of the building, electricians and plumbers must take special care when running services such as electrical cabling or gas lines through structural walls. The most convenient way to do this is to notch or drill directly through a stud, however, multiple notches compromise the integrity of the frame.
Every 32mm notch or drilled hole reduces the section of the stud by the same amount, compromising its overall capacity. Multiple notches in close proximity to each other will turn a code-compliant stud into an unsafe one.
The best way to deal with services in rooms with a high concentration of penetrations such as kitchens, bathrooms, or media rooms, is to plan a service cavity. A cavity can be formed by utilising deeper studs, double-stud walls with space in between, or batten timbers installed within the stud cavity that carry the services and are subsequently hidden from view.
A cavity adds to the overall timber consumption, but reduces the risk of compromise to the frame, and causes fewer issues on site due to the services running alongside rather than through the frame.
Soundproofing decisions are made within the wall, not on it
Soundproofing is one of those jobs that homeowners often believe can be added on to existing walls with relative ease. In most cases, this is untrue. Soundwaves travel not only through the wall, but also through the timber frame itself, utilising it as a flanking path, making alterations to an enclosed wall ineffective. The most effective way to soundproof a home is to utilise a deeper cavity with acoustic treatments such as acoustic batts or resilient mounts, and/or staggered internal and external stud framing. These treatments would be near impossible to retrofit onto an existing 90mm cavity wall.
A 140mm cavity wall with acoustic insulation, mounts, and/or staggered internal framing is a vastly better option to soundproof a home, especially for families or those building near heavily-trafficked roads or areas.
Prefabricated panels and keeping the frame dry before lining
Most people will never consider these two decisions when touring a show home. The first is choosing between prefab panels and on-site framing. Prefab wall panels are constructed in a factory under controlled conditions and are often much flatter than their on-site equivalents. This reduces the amount of plasterboard filling required, as well as the overall number of visible seams, creating a neater and more presentable surface.
The second decision involves leaving the frame to dry before lining it. Wet timber that is enclosed in plasterboard will warp and twist, often causing unsightly cracks along the length of a stud wall, which will be virtually impossible to disguise with spot putty or other fillers. It is important to leave the frame to dry, especially if wet weather is anticipated, as this will greatly reduce the likelihood of such issues. Good builders will always schedule roof and cladding work in accordance with internal lining schedules to ensure that the frame is as dry as possible at the time of enclosure.
All of these decisions are hidden from most people, who will generally only see the results of these processes in the completed house. They will see cracks along the baseboards, hear their neighbour’s dog barking at all hours of the day, notice how the walls bow out at an angle when viewing the house from an outdoor deck, or feel constricted in a house with low ceilings.
These are the details that most people will overlook, but they can have a large impact on the final result, and should be considered seriously before a single sheet of plasterboard is cut.