Month: September 2017

Categories
MicroArchitecture

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: ValleyWorkspace.org-BuildingMoistureStorage (PDF)
Also see “The Wetting and Drying of Timber Framed Walls“

Categories
MicroArchitecture

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.

Categories
MicroArchitecture

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: ValleyWorkspace.org-BuildingMoistureStorage (PDF)
Also see “The Wetting and Drying of Timber Framed Walls“