Household Moisture – Its in the Furnishings and Materials

Household moisture primarily resides in the building materials and furnishings in a house.  Think your big, damp mattress, for instance.
Damp materials in your house keep your relative humidity high.  And releasing humidity into the air means that moisture will eventually find its way inside your couch, or in other furnishings or building materials.
Here is a simple chart of the equilibrium relationship between moisture in the air (RH), and moisture in materials (MC), expressed as a percentage of the mass of the material.
This chart can be read as follows:  If you house averages 70% humidity, you can follow the 70% RH line and see that spruce wood (similar to pine), will have about 13% moisture content.  Given that your house will have thousands of kg of pine in it, this chart means there will be hundreds of kg of water in that material.  And the same with wallboard, insulation, soft furnishings, and your carpet.

For experimental purposes, or for learning with school kids, a simple hygrothermal (heat and moisture) model of a house can be built as so:

Read about our recent research with the Valley Community Workspace community group: (PDF)
Also see “The Wetting and Drying of Timber Framed Walls


Building Activity

How many houses are being built in New Zealand? And where?  This question and more can be answered using SHAC’s Building Activity app.


Damp Homes

Imagine, if you take a cold and damp house, and then wrap it in extra insulation and draughtproofing.  What do you get? A warm and damp house.  The extra insulation and draughtproofing reduce the air circulating in a house, which is a reduction of the ability for a house to dry itself.

How do we get a warm and dry house?  Capture the sun, add heating to the house, and add ventilation. This can be as simple as ensuring the windows of a house are open during the day, especially when it is sunny out.  Or you can add some sort of ventilation system that takes in outside air into the house.  Your heat pump does not do this – all a heat pump does is recirculate the damp air that is already inside your house.
On the whole, outside air is dryer than inside air, especially once it is heated to inside temperatures. This is why bringing outside air into the house helps to dry the house. There is some cost to heating outside air, but the benefit is a dryer, healthier house.  Also, if a ventilation system is used, this cost can be reduced if a heat recovery ventilation system is used. Of course using windows for ventilation is the cheapest option of all!

Psychrometric chart showing WHO recommended temperature and humidity (green+blue region), and room measurements for one week. Each point is average temperature and humidity for one hour. Different times of day are coloured differently.

Most of the moisture (>85%) in a house is in the furnishings and building materials in the house. Simply removing moist air once will not dry a house, as dampness will just evaporate from furnishings and building materials, and the air will quickly become damp again, within minutes. A damp house needs repeated flushing of the air within the house so that the furnishings and building materials within the house slowly begin to dry.
Read about our recent research with the Valley Community Workspace community group: (PDF)
Also see “The Wetting and Drying of Timber Framed Walls


The Pretty Good House

A Pretty Good House should:

  • Support the local economy. That means building with local labor, with locally available and/or produced materials, as much as possible.
  • Be commissioned following construction, and be monitored on an ongoing basis. If you don’t know, and to me it’s a strange use of the word, commissioning means testing how the house performs after it’s built.
  • Have operating costs that are minimal or reasonable.
  • Have R1.8-R3.6-R6-R10 insulation. Hopefully these numbers are obvious: they represent a “pretty good” level of insulation in a cold climate for sub-slab, foundation walls, framed walls, and roof or ceiling, respectively.
  • Measure 90-140-160-180 m2. These number are probably not as obvious; they represent an allotment of square feet of living space for 1, 2, 3, and 4+ inhabitants, respectively. It could be less — the national average is much more — but as a group we thought this was… pretty good.

What’s in and what’s out?

We came up with a list of what is in versus what is out of a pretty good house. What’s in:

  • Superinsulation.
  • 4 inches of rigid foam under the basement slab.
  • A service core for plumbing and wiring (à la Tedd Benson’s Bensonwood concept, also a feature of A Pattern Language (Alexandar, et. al.): keep services out of exterior walls, grouped for easy upgrades in the future.
  • Energy modeling (performed during the design process).
  • Adaptability/durability/recyclability. For more on this topic, see Alex Wilson’s blog, “Ensure Durability and Reuse Existing Buildings.”
  • An air leakage rate of no more than 2 ACH50. Not exactly Passivhaus, but… pretty good.
  • Good design. I was surprised it took so long for someone to mention this. A good house has to look good and feel good, not just function well.
  • An owners’ manual. I know that Michael Chandler has written about this. You get an owners’ manual with your car, DVD player, and electric toothbrush. Shouldn’t the biggest, most expensive, most complicated thing you own have an owners’ manual too?
  • Universal Design. Our population is getting older, and people are realizing that having a disability does not mean one’s lifestyle needs to be limited. For the most part, Universal Design is smart design.
  • Comfort. Recently I was at Chris Corson’s Passivhaus project on a cold day. There were no drafts, no cold spots in front of windows, and only a single Mr. Slim heat pump for the whole house. It was comfortable. I’ve been in $20 million dollar houses that were not comfortable (and probably insulated with fiberglass batts).

Keep it simple

What’s out:

  • Passivhaus under-slab insulation. 10 to 14 inches of foam? As great as many of us think the Passivhaus standard is, it’s still hard to imagine using that much foam under the slab.
  • Toxic/unhealthy materials. Duh.
  • Too much embodied energy. Spray foam is a great insulator, but it comes at a cost. Vinyl siding is cheap and (somewhat) effective, but it comes at a cost. Bamboo flooring comes at a (transportation) cost, and having installed quite a bit of it, I don’t think it’s all that great….
  • Diminished returns. The idea of the Pretty Good House is to find the sweet spot between expenditures and gains. When is enough insulation enough?
  • Complexity of structure. With modern living space “needs” and small lots come oversize houses. One way to reduce the apparent scale of the house is to chop up the roof with dormers, pepper the walls with bumpouts, and otherwise create places for ice dams, air leaks and extra construction labor and materials (see Martin’s blog,“Martin’s Ten Rules of Roof Design”). I’m guilty of frequently designing in dormers to the renovations and additions I work on, as a way to buy extra space while respecting the original architecture…but at least I’m aware that it’s a problem.

Source: The Pretty Good House


Addressing the challenge of climate change together, activists and designers

… Climate activism has primarily manifested as “Blockadia.”  Why? Blocking and shutting down bad projects is easier to organize around than efficiency or carbon pricing. And maybe that’s fine. Maybe it isn’t the role of activists to imagine and bring about a new world. Maybe that’s for policymakers, designers, engineers, artists, and entrepreneurs.

Source: Architecture and Climate – what critics misunderstand about climate activism


Hutt Shelter [2015-80]

The starting point for this design references the traditional timber framed barns once common in Canterbury. Occasionally you come across a barn nearing the end of its life, with bleached and weathered timbers. The roof framing is letting go, and a graceful curve develops in the ridge line as the building becomes more beautifully integrated into the landscape.
This building will be an ambassador for natural building. For many it will be their first encounter with these technologies. As such it should be relatable, distinctive, dignifying; a building that people can identify with. At the same time expressive of the materials used.
In this design the main materials are sourced from the nearby landscape. Wheat straw from the surrounding farmland; lime from Amuri for plaster; macrocarpa from farm shelterbelts for frame and cladding; bricks for the floor salvaged from the Canterbury earthquakes; and river stones for the sheltering wall along the south.

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Shingle Point [2015-77]

Shingle Point
Inspired by the jagged peaks of the Southern Alps and the timber boardwalks on our national walking trails. Shingle point looks to a regenerative future and harks back to simple timber settlers cottages. With native timber flooring, framing, sarking and cladding the intended structure would be formed from our natural resources. Reclaimed Totara heartwood is proposed for its inherent durability. This timber was highly prized by both the Maoris and the early European settlers. It needs no chemical treatment and can be oiled to retain colour or left to silver naturally. A faceted Greywacke stone plinth is also proposed to anchor the structure, form the seating and elevate the timber from ground moisture. These materials and the form are intended to blend into Methven’s built alpine vernacular and relate to the areas dramatic natural landscape.

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Snöhuttë [2015-69]

Snöhuttë is a bus shelter located on the out skirt of Methven, 47 Racecourse road, besides Ski Time resort. Its primary function is to serve as a shelter for tourist and locals waiting to head out to the local mountains for winter activities via bus transport. The shelter comfortably accommodates 20 travellers and their gear, whilst keeping them warm courtesy of the fire place within the feature wall that also doubles as a chimney. The shelter can also function between winter seasons as a communal space by transforming the entrance wall to create an additional covered outdoor area. Materials used to create the shelter are natural stone for the base and feature wall, rammed earth southern wall, and pine timber to create the inhabitable spaces with north facing glass windows. The sloped roof prevents snow from collecting on the roof, the covered entrance way provides an intermediate transition that combats the strong north westerly winds, and rest of the shelter is completely sealed to combat wild weather conditions of Methven.
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Cafouillis Shelter [2015-68]

Hey! so our design is made out of steel beams for the structure and correlated iron for the back cladding, the interior is lined with untreated timber, the interior bracing elements are also timber and are held together by stainless bracing (pictured in poster). Our design was inspired by the norwest arch, geodesic domes and also the dna helix.
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ONTRACK [2015-67]

ONTRACK is about bringing back Methven’s heritage. We will revive the railway by creating a shelter out of rail tracks.
The rails will form the structural frame of the shelter, and recycle materials from Christchurch such as: stone, timber and iron roofing will be used to create the walls, floor and the cladding.
The bus shelter is about 30m2, with 2 entries (one from resort, other one from the road), ski storage, covered seated areas and have great visibility on the road.
It is protected by timber panels that are hooked onto the structure and the shelter is positioned to receive the most sun in the morning but also to protect from the south and western winds.

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