A question that comes up over and over is, can I remove a wall in my house?
The New Zealand Building Act 2004 Schedule 1 allows existing walls to be removed without a building consent but there are around 5 exclusions. These include but are not limited to load bearing walls and wall bracing. Before attempting any work of this nature, building owners should hire a professional.
This is an overview on how residential roof structures disperse loads and the answer to this question varies depending on what type of construction has been employed when your house was built. We are only going to cover two types of house construction and these are the most common in New Zealand for roofing structures. The walls and foundations are demonstrated here as timber but other types are similar as the forces still track more or less the same. It is important to note that a weather board house and a brick veneer house are both timber frame construction and are not to be confused with solid brick or block.
The two common types are; trusses and pitched. Trusses are generally for residential, timber and produced in a factory using presses, while pitched roofs are built on site from individual pieces of timber cut and nailed in place.
If your house is pre 1950 it will most likely be a pitched roof system, while if it is post 1950 it could be a trussed system with trusses being widely used from the late 1960 on.
We will start with the trussed roof system as these are much more simplistic in there concept although the trussed system can be very complex and more flexible than a lot of people (even some builders) realise. The main thing to understand with trusses is they will span the entire width of a house without requiring any internal support. The distance trusses can span is easily 12 meters and for specific designs more than this although spans greater than 12 meters would be outside the scope of the New Zealand Timber Code requiring a structural Engineer to provide structural evidence to Council for the house design .
The trussed system
This drawing shows a trussed roof applied to a simple house. The trusses are shown in yellow as they are taking load from the roofing material as well as the load from people required for maintenance. The walls taking the load from the trusses are also shown in yellow as are the foundations and footings. The walls that show up in this drawing are basically the exterior walls of the building. It is important to note that while trusses normally transfer all the loads to the exterior walls there can be times when an internal wall may be used to support a truss such as a half truss which only covers part of the building width. You can identify trusses in your roof construction as they all have some form of strut system as shown in the above drawing (in this case the struts looks like the letter double u) there are other configurations. Trusses also have labels attached to them.
This diagram shows the the walls without the trussed roof and you can see that all the interior walls shown in green are non load bearing as discussed above. The trussed roof system is not only more efficient than a pitched roof, it also allows for interior walls to be arranged in any layout without having to worry about supporting the ceiling as the trusses also carry the ceiling loads. It would be possible to design a trussed roof residential building without any interior walls if it it wasn’t for the necessity of wall bracing.
Foundation to buildings with trussed roofs are also simplified. From this foundation drawing it can be seen that the sub-floor layout is very simple and again the loads carrying the roof loads (shown in yellow) are only on the outer rows of piles. The internal rows are carrying floor loads only.
Pitched roof system
The pitched system shown here is as we said, built on site from cut timbers and nailed together piece by piece. Instantly you can see that this system is much more complex and requires a lot of timber struts to transfer the roof loads down on to beams in the ceiling known as ceiling runners. Ceiling runners used to be called strong backs in the early days. These ceiling runners then span between internal load bearing walls which run across the building. Walls running length wise can also and often are load bearing as they take the loads from struts that can come from the ridge board at the very top of the roof as well as sometimes struts coming from the rafters at the mid point which then slope towards the middle of the ceiling where they are fixed to a plate directly over a longitudinal wall near the center of the building. Ceiling joists (which hold up the ceiling lining usually require ceiling runners as well. In this drawing the ceiling joists are supported by the ceiling runner that also supports the struts from the rafters. The usual give away of a pitched roof is when you look into the roof space you see pieces of timber going in all directions and often no one roof space will look the same, as each builder will have his own way of constructing this type of roof.
This drawing shows the walls of the same house as the trussed roof system but clearly indicates the limitations of the pitched roof system. All the walls except one (shown in green) are to some degree or another load bearing. I say one degree or another because the longitunal internal walls (as per the long exterior walls) carry a constant load from the roof along it’s length while the short interior walls running across the building may only have a post or double stud inside them to take the load from the ceiling runner above. What this means is part of these interior walls could be removed but not all of the wall while the longitudinal walls almost always require a beam to replace that part of the wall that has been removed.
The sub floor and foundations for the pitched roof also gives away that your interior wall is load bearing as it will either have additional or double joists directly below the wall or an entire row of piles dedicated to the wall (usually a longitudinal interior wall) also you may sometimes find an isolated pile that looks out of place to the rows of other piles and this most certainly will be carrying some form of load from above. You can see in this drawing that there is a dedicated row of piles (in yellow) running roughly on center and this row is taking the load from the longitudinal interior wall directly above it and down the center. In addition to the dedicated row of piles you can see some special joists (coloured yellow) and these are positioned directly under the interior walls that run across the building and are picking up the loads coming down through these walls via posts in the wall and ultimately from the ceiling runners which in turn carry loads from the roof rafters.
In summary
Deciding which walls are load bearing and which aren’t can be a little daunting and I’ve even heard of professional wondering around banging walls and announcing if a wall is load bearing or not, but if you don’t look up in the ceiling space and identify what type of construction is up there (truss or pitched) then it is nothing more than a guess and it could be a very expensive guess. Before you do any demolition, identify the load bearing walls properly.
When it comes to removing walls, any interior wall can be removed and you don’t always have to have a beam below the ceiling. New beams can be installed above the ceiling and in some cases reasonably easily. This method always looks great and gives you home that professional look where it looks like it had been built that way. You will require a building consent to remove or alter load bearing walls.
The other method which can be used in some instances is using a truss to hold up the original roof especially when adding onto the side of an existing house. A girder truss can be used to support an existing roof whether the original roof is trussed or pitched. This is the method I used for the alterations to the Lockwood house at Bombay and you can see how this is done if you check out my web page www.ait.kiwi.nz “current work”.
I hope this helps those people who are not in the industry but would like to understand the mysteries that lurks above their heads and give these people a little more confidence with this issue that even some professionals (builders included) argue over.
Ross Newby Architectural Designer – Design 3 LBP.