Gab Learns The Building Envelope

Lesson Four: Building Envelope

What is the building envelope?

We are wrapping up the last three episodes to discuss the whole building. The Building Envelope / Enclosure. We are not talking about your standard DL paper envelope. No, we are talking about the Building Envelope – anything that separates the inside from the outside, starting with the roof, the walls, windows and the underground.

Why should we think of the full enclosure?

Simply put, it is really important to live in a warm, dry and comfortable home. Not only is this more pleasant but there is also a strong correlation with the health of the occupants. Let’s think of something we can (all) relate to – building a burger – you’d be crazy to leave the bottom or top of the bun off or forget to add extra cheese on the patty. Same goes with your building – it’s important to think about everything that ties together; the walls, the floors, the windows…

Who specializes in Building Envelopes?

Well, Oculus does (of course). Typically, façade engineers focus on the vertical surfaces of a building or curtain walls (glass all the way up the side of a building) and are contracted to design the curtain wall and windows. Everything else is left to the architects to design – the layout and aesthetics of the building, however the science behind it isn’t always fully considered, and neither are the junctions between. Building scientists however focus on the complete envelope ensuring that it works well and works properly (Contact Oculus on 027 358 8463).

So, what are the different components of the building envelope?

The top three components that make up the building envelope are:

  1. Roof – the roof is designed to keep the inside in, and the outside out. It requires insulation in the assembly to ensure heat doesn’t escape.
  2. Walls – the walls are designed to keep the inside in, and the outside out. The walls protect insulation, cladding, gib board and studs.
  3. Underground – the underground is designed to keep the inside in, and the outside out. Basements aren’t very common in NZ; however overseas basements are used as additional rooms or storage.

As you can see the 3 main components of the building envelope are all designed with the same objective – to keep the inside in, and the outside out.

If you are buying a house, how do you know if the building envelope is sound?

Without opening things up (walls) it can be hard to tell just what you are looking at.

However, here are a few things to pay attention to:

  1. Conditions such as bubbling paint – however often when an owner is selling these conditions would likely be topped up with a new lick of paint etc).
  2. Ask the right questions – check previous building reports if they are available to you. Has there been carpet recently laid? If so, check the condition of the flooring and underground insulation – if there is any (ensure there are no preexisting moisture issues).
  3. Check the roof – access the hatch, look at what is happening in there. If you see mould, water or any stains this is a bad. The insulation should be on the ceiling, and if there is none, factor that you will need to install this yourself. If the insulation is stained or mushy then there are probably issues.

If the walls are hard to indicate how sound the building envelope is, how do you tell without taking a hammer to the walls?

  1. If the walls are warped this is a big giveaway that there is likely moisture in the walls. Even if you don’t see warped walls, it could be that the walls have been recently painted (another tell-tale sign).
  2. Check the windows – look at the framing, are there gaps in the corners? Is it single glazed or double glazed? Not sure? Quickest way to check is to look at the window, if you can see a space / gap inside the window between the two pieces of glass this is double glazed.

SIDE NOTE: Low E coating is generally bought with the window; however, you can buy post installation of the window. The coating allows the building to be warmer in the winter, and cooler in the winter as it reflects the sun out in the summer. Lesson here? Always wear your sunscreen – windows included.

  1. Underground – check the underground. If there is a carpark / carport built into the hill, check if it smells wet and musty. If you see water leaking or staining the walls or green stuff (gross) in walls it’s a sign there is little to no waterproofing on other side of wall. These problems are very difficult to mitigate post construction.

So, what about cracks around door frames, or in walls?

Buildings are built to withstand environmental impacts, and as such building movement does occur. If there is are cracks tracking diagonally in a corner of a room, this is typically a result of building movement. Cracks that appear around doors is due to thermal movement because the door frame shrinks at a different rate than the rest of the walls. Movement (expansion and contraction) occurs at different rates, and a well-designed building would account for this so it shouldn’t be an issue. However, even if cracks are present, they can be accommodated with tapes or sealants (heeeeey Bunnings) which stretch as the building moves.

Do apartments differ from housing?

Definitely. A house has 6 surfaces to lose heat through however in an apartment there may only be one or two walls for energy to escape. The insulation between the connecting walls shouldn’t matter as much because each apartment should be sufficiently heated which reduces the amount of warm and cold surfaces meeting.

To summarize, the building envelope (roof, wall, underground) is designed to keep the inside in, and the outside out. There are various ways to check how sound the envelope is on an existing property, and many questions to ask before buying/renting or even planning to build. So now we’re clued up on the building envelope – let’s put it to post.

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