Compare Western Red Cedar to Thermally Modified Hemlock SidingWritten by Chris Nolan on
For decades, Western Red Cedar has been the gold standard for softwood siding for builders, designers, and homeowners. And why not? Cedar siding is naturally beautiful, performs well and was readily available. Well, there’s a new sheriff in town, Thermally Modified Hem Fir (Hemlock) siding. And you may want to check it out.
Mataverde Thermally Modified Hem Fir is available for siding, fences, trim and more
Compare KD Western Red Cedar Siding to Thermally Modified Hem Fir Siding
What is the difference between kiln dried wood siding and thermally modified wood siding?
Kiln Dried Wood
Kiln drying lumber is a great way to get some of the moisture out of wood to shrink it and help it become more dimensionally stable. Green lumber is placed into a kiln at pre-determined temperatures for a set number of hours (or days) based on best results for a particular wood species. Finding the right ‘recipe’ for kiln drying various wood species has been developed, through trial and error, for a long time. This is called the kiln drying schedule.
Thermally Modified Wood
Thermal modifying wood is like kiln drying, except moisture is added, and the wood is heated to higher temperatures. The moisture keeps the wood from misbehaving during the drying process. The higher temperatures ‘cook’ the sugars out. This makes thermally modified wood more resistant to insect damage and more decay resistant. The moisture helps the wood become more dimensionally stable.
When softwood lumber species are thermally modified, it usually makes the wood harder, more rot resistant, and more stable (less movement) than the original wood. On the downside, it usually makes the thermally modified wood a little more brittle than the original wood. However, thermally modified hemlock performs better in many ways.
The unique process used for Mataverde Thermally Modified Western Hemlock (Hem-Fir) employs a vacuum kiln. The vacuum kiln creates increases the pressure, so it takes less heat to ‘cook’ the sugars out of the wood. This thermal modification process uses much less energy. And the finished siding product is beautiful, and exceptionally stable.
Aesthetics and the real wood siding beauty pageant - Cedar vs. Therma Hemlock
Beauty is in the eye of the beholder. Most people find Western Red Cedar to be gorgeous.
Western Red Cedar siding installed on a coastal rainscreen siding project
Thermally Modified Hem Fir siding is beautiful, too. Because the thermal modification process of Hemlock tends to darken the wood slightly, you will find the color to be more consistent than Cedar. Both of these two softwood siding options look great. You decide.
Thermally Modified Hemlock siding can be finished beautifully with oil-based stains and paints
Availability and Affordability of Cedar and Thermally Modified Hemlock Wood
Nowadays, Red Cedar isn’t always as readily available as it once was. Sometimes red cedar, especially the upper grades, are quite difficult to find. And when supplies get low, cedar prices tend to rise. Sometimes quickly and often steeply.
Thermally Modified Western Hemlock (Hem-Fir) on the other hand, is readily available, and the pricing is not as volatile as Red Cedar, especially in the upper grades, like A grade and C+ Better. Because thermally modified hemlock is more obtainable, it is usually ready for your project a lot faster, and the pricing is less susceptible to sharp price increases.
Strength Comparisons Red cedar vs. Thermally Modified Hem-Fir
Thermally Modified Hemlock (Hem-Fir) is much stronger than Western red cedar. Scientific testing confirms that Therma Hemlock is almost twice as difficult to break than western red cedar (Modulus of Rupture test). Thermally modified hem-fir is also 70% less brittle than red cedar (Modulus of Elasticity test).
The winner: Thermally Modified Hemlock
Thermally modified hem-fir siding
Hardness Testing of Red Cedar and ThermaWood Hem Fir
When measuring the hardness of wood using the Janka hardness test, thermally modified hemlock is almost twice as hard as red cedar.
It takes 622 lbs. of pressure to put a .444” diameter steel ball halfway into a piece of thermally modified hemlock.
It takes only 350 pounds of force to embed the same steel ball halfway into a piece of red cedar (very soft).
The winner: Thermally Modified Hemlock
Dimensional Stability of Red Cedar compared to Thermally Modified Hemlock
When you hear people discussing wood ‘stability’, they are referring to the dimensional stability of wood. All woods will expand when moisture is added. And all wood will shrink when moisture is taken away. Dimensional stability testing measures exactly how much each piece of wood will expand (swelling) and contract (shrinkage) when water is added or taken away. Thermally modified woods are almost always far more stable than their non-modified counterparts.
Kiln Dried Vertical Grain Western red cedar is very stable. It shrinks about 2%. Flat grain red cedar, however, expands up to 5%.
Thermally modified hemlock is significantly more stable than Western red cedar. Therma hemlock exhibits exceptionally little expansion and contraction. And because hemlock is thermally modified in a vacuum kiln, the results are very impressive.
Vertical grain thermally modified hemlock siding shrinks 1.5% as it dries. Vertical grain thermally modified hemlock siding swells up to 1.8% as it picks up moisture. That is why it is considered highly stable.
- For example, when you take a piece of 1 x 6 of vertical grain thermally modified hemlock, it will expand or contract much less than 1/8” over the face of the board.
- A piece of 1 x 6 Vertical Grain Western Red Cedar will expand just under an eight inch.
- A piece of 1 x 6 flat sawn Western red cedar may shrink more than a quarter inch.
The winner (by a landslide): Thermally Modified Hemlock
Clear vertical grain Thermally Modified Western Hem Fir has a lovely range of color tones
Durability of Red Cedar vs. Thermally modified Hemlock siding
Durability testing measures how long a particular wood species is expected to last when subjected to insects (like ants and termites) and various fungi that will cause wood to rot and decay.
Western Red Cedar is rated between moderately resistant to resistant against both insects and decay. Moderately resistant means an expected service life of 10-15 years. Resistant means the wood should hold up for up to 15 -20 years.
Because thermally modifying Hemlock ‘cooks’ the sugars out, it is rated ‘very resistant’ to both insects and decay. Under normal conditions you should expect a service life of 25+ years with thermally modified hemlock.
Whether you are installing your siding in a traditional ship lap or tongue and groove (T&G) profile, or prefer a rainscreen siding design and installation, both species are very good options to consider.
Clear-cut winner: Thermally Modified Hemlock
Interested in learning more about rainscreen siding design and installation?
Download the "Ultimate Guide to Wood Rainscreens" today.
Fastener Withdrawal of Western Red Cedar vs. Thermally Modified Hemlock
The pull-out strength of Western Red Cedar and thermally Modified Hemlock are almost identical for nail pull-out. Thermally modified hemlock has slightly higher strength for screw pull-out than Western Red Cedar.
Winner (by a nose): Thermally modified hemlock.
Compare Mechanical Properties of Thermally Modified Hemlock and Western Red Cedar
Overall, you have two very beautiful softwood siding options to choose from. Both species perform well in a rainscreen siding system or in a tongue and groove siding profile. Please check out the actual test results and mechanical properties and performance criteria of Western Red Cedar vs. Thermally Modified Hemlock (Hem-Fir) chart below.
Looking for some great rainscreen siding design ideas?
Download the Featured Rainscreen Siding Projects Portfolio today.