August 17, 2018: Adamant About Eaves

For the last couple of months Cintia and I have been working on an affordable housing project in Queensland. I’ll give an update on that in a minute but before I do I’d like to take a brief side-track and talk about the importance of a good roof overhang.

Is this the height of contemporary design? (Image Source: freshome.com)

Is this the epitome of contemporary design? (Image Source: freshome.com)

You see this sort of thing all the time on shows like ‘Grand Designs’ and in glossy magazines promoting the latest trends in style and fashion. It’s usually described as ‘Modern’, ‘Sleek’, ‘Minimalist’ and ‘Stylish’. This is rubbish! What it should be called is ‘Dumb’, ‘Stupid’, ‘Idiotic’, and ‘Moronic’.

From the viewpoint of energy-efficiency, sustainability and durability there are SO many things about this style of home that I could criticise, from the acres of glass and the tons of steel and concrete to the flat roofs and lack of insulation or consideration for climate. But the thing I want to focus on today is the lack of proper eaves (or roof overhangs).

As every bushie knows, if you’re going to be exposed to the elements, you need to have a good hat and boots. In the building arena this translates to a good roof (with adequate slope and overhang) and solid foundations that lift the building up out of any potential moisture problems. It’s just good-old common sense, right?

But, as we all know, common sense is not that common. So I was surprised and delighted to find the following passage in the Installation Instructions for James Hardie Industries ‘Hardieflex’ Eave Lining product

Protection from the environment plays an important part in the thermal comfort and durability of houses, in both cool and hot climates. A simple method is to extend the roof well over the external walls of the typical house to form an eaves overhang or, if further extended, a verandah. 

Incorporating eaves and overhangs provides a number of important benefits, into your structures such as:

  • shading walls from excessive solar gain
  • keeping direct sun off the window glazing
  • allowing windows to be left open for comfort ventilation while still providing shelter from rain and
  • protecting large areas of walling from rain, keeping wall surfaces relatively dry and free from staining and mould growth.

Unfortunately, the recent trend to reduce the width of traditional eaves and, in some instances to eliminate eaves altogether… deprives the home owner of these benefits and increases running costs of comfort measures, such as air-conditioning.

I couldn’t have said it better myself (although I would add that the correct amount of roof overhang can be calculated to provide solar gain for winter warmth and shading for summer cooling – see our section on Passive Solar Design for more information).

As far as I’m concerned, the correct amount of roof overhang is absolutely essential to good building design. So the next time you see or read something that describes a ‘Modern’ home with a flat roof and no eave overhang as ‘Stylish’ or ‘High Design’ I suggest you do what I do and shout ‘RUBBISH!!!’ at the television or magazine in question.

Project Update

Speaking of roof overhangs, Cintia and I have spent the last few days installing the eave linings on the house we’re building.

Today's progress photo showing the eave linings and furring strips.

Today’s progress photo showing the eave linings and furring strips.

We’ve also been adding furring strips (or spacers) to the exterior walls to provide an air space between the sarking and the cladding. This does two things…

  1. It creates a space between the sarking (the silver fabric wrapped around the exterior walls) and the cladding (which will be corrugated Colorbond). This allows the reflective surface of the sarking to effectively block radiant heat. If the cladding were installed tight to the sarking heat would be conducted directly from the corrugated metal through the sarking and into the walls.
  2. The air space also allows air to move behind the cladding. When the sun hits the corrugated metal and heats the air behind it, the warm air can rise up in the air space, vent out the top, draw cool air in at the bottom and help to keep the walls cool.

If you look closely you can see a strip of insect screen along the bottom of the wall. This will cover the air gap at the bottom of the wall and help stop too many spiders and wasps from taking up residence in our walls.

We'll wrap the screen around the furring strips so it covers the gap at the bottom.

We’ll wrap the screen around the furring strips so it covers the gap at the bottom.

The part we haven’t done yet is to add vents in the eave linings. Below is a picture of a typical Australian roof with a dark, hipped roof (shaped like a pyramid) and no vents in the eaves.

A typical dark, hipped roof with no eave vents.

A typical dark, hipped roof with no eave vents.

This is an INSANE way to build a roof in our hot climate. A dark-coloured roof absorbs way more heat than a light-coloured one and a hipped roof is much harder to ventilate than a gable roof (one shaped like an open book), especially if you don’t install any vents in the eaves or near the ridge.

Ideally you want both eave and ridge vents so that heat in the attic can rise up and out the ridge vent and draw cool air in from the eave vents. In our case we’ll have vents high up in the gable ends of the roof and small, round vents in the eaves like these.

We'll have vents like these every 1200mm for the length of our eaves.

We’ll have vents like these every 1200mm for the length of our eaves.

So, with our light coloured roof which has insulation blanket under it and our well-ventilated eaves and attic, our house will have a much better chance of staying cool in a hot Queensland summer than your typical Australian home.

3 comments to August 17, 2018: Adamant About Eaves

  • Wow Andy, I kneel and bow to you o god of common sense building design and construction! I’ve just read your last few newsletters on the QLD project. Great to get an insight on week to week progress and see the photos.
    It’s such a pity that we in the trade are not taught how to build properly, also why and how good building design and construction helps those that eventually live in the home! Our teachers and employers are always focused on the “minimum” requirements and the “least” expensive options. And of course old habits that are passed on from builder to builder.
    I’m so happy to be connected with you and learning along the way!
    All the best to you and Cintia in the coming weeks as you work through the project.
    Regards,
    Richard Hamilton

  • Very interesting , as always – your progress is amazing – well done !

  • Keep safe & well in this big adventure , cheers! L.

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