Timber Frame Pros Cons

[SteamyTea]

Just now, nod said:

We are paid to go back several times to sort out the cracks 

Does anyone get paid to find out why the cracks are happening?

[Declan52]

The first TF homes will built around 2002 where a piss take. We built the founds all in one go , about 20 sets of semis, and the timber frame company came out and measured up each plot. Not one frame did they get right. Most where too small and every single one was out of square and plumb so by the time we got to the wallplate height on the 2nd story there was near enough no cavity that you had to either cut the lip of the catnic or the back of the soldier course over the windows to get them in. 

Even though we had bonded it out in the red brick every window and door wasn't brickwork measurements. Cill heights and widths where all wrong. The site joiners spent more time altering each frame than doing their own work. 

More recently the brother in law moved into a  TF house built around 2010 that had zero insulation on the gable wall. He couldn't figure out why his house was so cold. 

And for some balance I have seen block and brick houses that would bring tears to your eyes. Houses brick bonded out so wrong that the perps have moved that much that they ended up with a brick extra across the front. Walls so out of plumb and I mean maybe 100mm from floor to ceiling that you side step going by as they look like they are going to topple over. Lead trays put in to high so you end up with a soaker near 2ft high going up a wall. 

It's scary some of the things you see when your working on building sites.

[SteamyTea]

4 minutes ago, Sensus said:

That's the 'decrement delay', due to thermal mass, that you're seeing.

I think you have misread the charts.

They show distribution, not a time series.

So basically they show how often a temperature happens when the external air temperature is the 'bin'.

The reason for this is that housing is not a steady state situation, temperatures, irradiation and windspeeds are constantly varying, and that is before you put in the effects of rain and evaporation.

I think the problem is that most people, including me 20 years ago, assumed that mass was the governing factor.

This axiom is wrong, it is the material's thermal characteristics that govern, so is a combination of volume, density, thermal conductivity, heat capacity, installed shape, exposed area and other things.

[Jeremy Harris]

6 hours ago, Sensus said:

 

For a thermal element, it's Kj/m²K

 

 

That's just a measure of heat energy per unit area, and has nothing to do with mass, assuming that what you really mean is kJ/m²·K (i.e. kilojoules/square metre · kelvin)

 

6 hours ago, Sensus said:

 

For a building as a whole (albeit this needs to be treated with caution, as an entire building does not respond as one homogeneous and uniform element), it's simply Kj/K.

 

 

kJ/K (not Kj/K, that has different meaning) is just a measure of energy per unit temperature, i.e. heat capacity, as kilojoules per kelvin.  Again there is no unit for mass, or volume expressed here, so how can it relate specifically to mass?

 

6 hours ago, Sensus said:

Ironically, in your leading post on the linked thread, you'd provided the dots... you just hadn't taken the final step of joining them up (and in fairness it's not as if there are actually that many of them to join!). I haven't done more than skim read the rest of the thread - I lost interest when I saw that the basic premise was so flawed - but I assumed that someone would have drawn this to your attention further down?

 

As you pointed out in your first post on the linked thread, mass on it's own isn't much use; neither is specific heat capacity. But you simply need to multiply the two together and ... bingo, you have thermal mass!

 

I'm sure I don't need to point out the basic algebra to you that when you are multiplying mass (kg) x specific heat capacity (j/deg. C/kg), the 'kg' simply cancels itself out and becomes j/deg.C (or Kj/K, if we want to use more convenient units, and Kelvin in place of Centigrade).

 

If you look at your own link, above, you'll see the next item down on the sidebar to the left (the sidebar titled 'building physics') tells you everything you need to know:

the thermal mass (Kappa value) of a thermal element is simply the sum of the mass of each sub-element, multiplied by the specific heat capacity of the material.

 

If you want to work out the thermal mass of an entire building (as above; with caution - it should only be used as a rough indicator or comparator, since there will be localised effects within the wider design), you'd simply be adding up the totals of the specific heat capacity of each material used, multiplied by the amount (mass) of that material present in the structure.

 

In simple terms, 'decrement delay' is an effect, not a cause... and it depends on the thermal mass (along with other factors).

 

 

Decrement delay is clearly a measurable effect, that's clear.   The cause and influencing factors that impact on the measured decrement delay is also clear, it is a fairly complex function of the thermal resistance of the fabric elements, the heat capacity of the fabric elements, the ∆_T across each fabric element, and the rate of change of temperature across them, with respect to time. 

 

Architecture seems to have chosen to misuse the language of science, so misleadingly refers to heat capacity as "thermal mass", in whole building terms.   "Thermal mass" is just a pseudo scientific term, that seems to have crept into common usage within architectural circles, but that does not make it in any way correct, from a scientific perspective.  The very fact that there are no units of either mass or volume used to define it, is a clear indication that it is a mythical property. How is it possible to examine the elements of the fabric of a building, and calculate the physical properties of thermal mass, to determine how any particular building may behave, when the supposed measurement makes no reference to mass (or volume, if preferred)?

 

Heat capacity can be defined for the elements of the fabric of a building, or anything else, by relating heat capacity, J/K, to either volume or mass.  The former gives the volumetric heat capacity of a material,  the latter the specific heat capacity of it.  For completeness we can also define material heat capacity as the molar heat capacity, although that has little use in building science.

 

If we wish to determine the thermal time constant of a building, which is probably the physical property that comes closest to how many people view this topic (i.e. how quickly, or slowly, does the temperature inside the building increase or decrease with a step change in outside surface temperature) then we can use the following measurable and easily defined parameters:

 

• Either the specific heat capacity (if we know the mass of each fabric element), or more usefully the volumetric heat capacity (as we will have the dimensions, and hence volume, from the drawings), for each material used.
• The thermal resistance of the materials that make up the external structure.
• The thermal resistance of the junctions between those materials that make up the external structure.
• The length of the heat flow path through each material (may be multidimensional)
• The magnitude of the temperature differential between the external surface and the internal space within the building.
• The rate of change of temperature on the external face of the structure.
• The volume of the building
• The total heat capacity of the materials that make up the internal structure.
• The thermal conductivity of those materials, which determines the rate at which they release heat into the air in the building, or absorb heat from it.

 

[SteamyTea]

1 minute ago, Sensus said:

11 minutes ago, SteamyTea said:

I think you have misread the charts.

 

Probably. Without context and a full explanation of the experiment, they're pretty meaningless.

Well the context is there.  You don't really need to know it to read the charts, but for more clarity, the experiment was 3 identical translucent boxes, each with 3 identically sized blocks of different materials in them.  They sit outside, in the weather, and temperature readings are taken every minute.

Then the fun of creating generalised rules, via statistical analysis happens.

5 minutes ago, Sensus said:

It's the thermal mass that's the governing factor

As @JSHarrisasked, and I teased about, what is the SI unit for thermal mass? I know the answer, but without others knowing it, confusion will continue.

7 minutes ago, Sensus said:

I think the root cause of the misunderstanding is that people are reading 'thermal mass' as simply meaning 'the mass

I think the root is deeper than that.  Many people assume that mass is weight, and when we have purchased things in the past, we associate weight with quality.  Now there may be some truth in that for some products, but it is not true for many industries.  Aviation and hiking being two extremes.

 

[Thedreamer]

@SteamyTea - this thread is a bit too scientific for me.

 

But I'm interested in the topic.

 

What is the principle with storage heaters, if you had two heaters one with timber inside and one with concrete, both heated with the same energy.

 

What happens next.

 

I take it the heat that entered the surrounding environment would be the same over a period of time, but would the one with concrete hold the heat and release it more evenly?

 

[SteamyTea]

One last chart to show how little difference the materials make.

This one shows that the distribution of material temperatures is very close to external air temperature, even though the mass of the materials, and there thermal characteristics, are all very different.

I have not looked at the probability of error, just that the slope of the lines are very similar, but I estimate that they are at the 99.99% level.

 

[SteamyTea]

9 minutes ago, Sensus said:

Out of interest, what would you prefer we call it

I know what I call it, and it is the correct term.

Thermal Inertia I (that is italicised and capitalised i)

8 minutes ago, Thedreamer said:

What is the principle with storage heaters, if you had two heaters one with timber inside and one with concrete, both heated with the same energy.

 

What happens next.

One may well catch fire, but if you limit the temperature then there is not a great deal of difference

 

These are the figures for my experiment.

Material	Volume /m3	Mass /kg	Density /kg.m-3	SHC kJ/kg/K	Thermal Conductivity	U-Value	Notes			I
PU	0.0017	0.06	35	1.4	0.2		Boxes moved on 25/06/2018			3.143621
Timber	0.0017	0.88	518	2.3	1.8					46.29318
Concrete Brick	0.0017	3.83	2253	1	1.1					49.78188

 

You can see that Timber and concrete have very similar I values

Edited September 7, 2019 by SteamyTea

[Thedreamer]

4 minutes ago, SteamyTea said:

I know what I call it, and it is the correct term.

Thermal Inertia I (that is italicised and capitalised i)

One may well catch fire, but if you limit the temperature then there is not a great deal of difference

 

These are the figures for my experiment.

Material	Volume /m3	Mass /kg	Density /kg.m-3	SHC kJ/kg/K	Thermal Conductivity	U-Value	Notes			I
PU	0.0017	0.06	35	1.4	0.2		Boxes moved on 25/06/2018			3.143621
Timber	0.0017	0.88	518	2.3	1.8					46.29318
Concrete Brick	0.0017	3.83	2253	1	1.1					49.78188

 

Maybe timber was not best example, prehaps a different light weight flammable material.

 

When you say limit the temperature, do you mean the temperature of the element producing the heat? I.e. the three would have different temperatures?

[Jeremy Harris]

4 hours ago, Sensus said:

 

Correct.

 

You're getting hung up on the name... as per my post immediately above, thermal mass is a thermal characteristic, not a mass characteristic.

 

The term 'thermal mass' is simply a bit more zingy than 'specific heat capacity x mass factor', which is why we (not just Architecture, though I recognise that you hate Architects with every fibre of your being) call it that for convenience.

 

Out of interest, what would you prefer we call it, assuming that you accept that, for convenience, it's expedient to attach a simple label to the combined characteristic of mass and specific heat capacity (which I think we're all agreed are pretty useless,  taken independently from each other)?

 

 

Titles of units are critical, and not to be taken lightly.  It's why we have strict rules on unit definitions in every measurement system used around the globe.  The SI system even has clear rules on how unit definitions, and their modifiers, should  be spelt, for the sole purpose of reducing the chance of confusion or misunderstanding.

 

The unit titles you've quoted do not define "thermal mass", and make no reference to mass at all in their referenced units, so the use of the term mass is highly misleading.  Like it or not, people regularly confuse mass with weight, probably because we buy stuff in units of mass, but use weighing devices to measure them.  Weighing devices don't, of course, measure mass, they measure force, it just so happens that it's convenient (at least for those of us living close to the mean radius of the Earth) to use the  gravitational force exerted by a mass as an analogy for mass. 

 

This does mean that, when weighing devices are used as an estimate of the mass of goods, people living closer to the mean radius of the Earth get less goods for their money than those living further from the mean radius of the Earth.  If there was a shop on the ISS, then scales would be a meaningless way of estimating mass, as they would read zero, no matter how much mass was placed on them.  This is probably a pretty good way  as any of demonstrating why precise terminology is essential when referring to anything that can be measured.

 

The most useful practical measure for the thermal comfort level of a building is probably the thermal time constant, how quickly or slowly it responds to a step change in outside temperature.  I think this may well be what many think of when the term "thermal mass" is used.

[Jeremy Harris]

21 minutes ago, SteamyTea said:

I know what I call it, and it is the correct term.

Thermal Inertia I (that is italicised and capitalised i)

 

 

Thermal inertia is pretty much the same thing as the thermal time constant, in practical terms.

 

Worth noting that the heat capacity of a material (either volumetric or specific) isn't a reliable indicator as to how well it may help stabilise temperature.  Thermal conductivity (for internal materials) or thermal resistance (for materials within the fabric) is at least as important, as we need to get the heat into, or out of, the material within a useful period of time.  Having a high specific heat capacity isn't any use if it takes a very long time for heat to flow into, or out of, the material.

 

6 minutes ago, Sensus said:

 

Only if you're at the extreme Aspergers end of the autistic spectrum.

 

For most people, titles (of anything) are just titles.

 

This has nothing at all to do with any personality disorder, it is just simple science.  If we were sloppy about units, and the ways in which those units are defined, then we would not even be able to trade with each other, let alone design and build structures.  Humankind has spent millennia defining, and refining, units and their definitions; they are key to everything we do.  When we get unit definitions wrong it often has serious consequences (for example, the Gimli Glider, where confusion between two units of mass led to an airliner full of people running out of fuel in mid-air).

[LA3222]

This thread turned heavy pretty quick ?

 

Thermal mass just seems to be one of those never ending arguments.

 

The only one that concerns me is cost comparisons between the build methods.  It was mentioned earlier that BB is cheaper than TF - but I've read loads of other articles which generally conclude there is very little to separate them?

 

I think I'd have preferred BB, but to get the desired U Value would have resulted in wall thicknesses that would have given a medieval fortress a run for its money!!!

[nod]

1 hour ago, SteamyTea said:

Does anyone get paid to find out why the cracks are happening?

Yep 

With timber frame it’s shrinkage

How ever dry it is there’s always moister in the timber then added moister from wet trades

On the commercial TF we add expansion joints  all over the place and simply caulk them in 6 months later 

People would want that on there nice new houses 

 

[Jeremy Harris]

7 minutes ago, Sensus said:

 

I hate to break this to you , JS.... but we've been successfully cobbling together buildings (and trading with each other, for that matter) for far longer than we've had internationally recognised units of measurement.

 

The difference between Architects and Scientists is that the Architects have long ago figuired out that you can't define to the Nth degree the performance of a building that is operating in very variable environment, serving beings with very variable levels of personal comfort, so there's no point in losing too much sleep trying.

 

Perhaps that just means that we're pretty relaxed about sloppiness?

 

 

I'd argue that trade has always depended on units.  Goods have always been measured in some way when offered for sale, and we have records of those units going back to pre-Roman times here in what is now the UK.  The unit of wine volume for example, seems to have been a standardised amphora.

 

Without measurement units, how did the ancient Britons ensure that their chariot wheels fitted the axles, or that the wheels were even the same diameter?  The units may have been crude, and poorly defined, but even the Old Testament uses defined units to describe physical properties, for example, “And this is how you shall make it: The length of the ark shall be three hundred cubits, its width fifty cubits, and its height thirty cubits.” (Genesis 6:15)

 

How did the ancient architects of the pyramids of Giza mark out and build them so relatively precisely, if they didn't have defined units? 

 

[Jeremy Harris]

4 minutes ago, nod said:

Yep 

With timber frame it’s shrinkage

How ever dry it is there’s always moister in the timber then added moister from wet trades

On the commercial TF we add expansion joints  all over the place and simply caulk them in 6 months later 

People would want that on there nice new houses 

 

 

 

I suspect that the biggest cause may be just loads of moisture being introduced into the building after it's sealed up.  The amount of water that was literally running down the inside of the windows after our house had been plastered was staggering, and the timber must have absorbed a lot of that.  When it dried out it then shrank back a bit, causing shrinkage cracks that I had to go around and fill.  The movement stopped after about 6 months or so, as the humidity level in the timber stabilised, I suspect.

[joe90]

A pro for b@b, our build was b@b and shed loads  of moisture after plastering, we suffered just a couple of hairline cracks after 6 months, the decorator stated our new build had less cracks than any other new build he had painted (as I have said before, we had a brilliant builder).

 

Regarding being hung up, or being pedantic about terminology, it’s either right or wrong, my pet hate is people saying “ah yes, but you know what I meant”, NO I know what you said (which was wrong). I used to use the term “thermal mass” but now say we have a “heavy house”. (Then explain that thermal mass has no units to be measured).

[SteamyTea]

31 minutes ago, Sensus said:

So if you multiply the specific heat capacity by the density you get:

You have to include conductivity as well. Do a dimension analysis on what you have done and you will see it does not make sense.

31 minutes ago, Sensus said:

For most people, titles (of anything) are just titles.

Yes. And this is why we have confusion like this.

It is not hard or difficult scientifically or mathematically, but by just giving things random names, or titles, or units, nothing can be worked out properly.

 

You may not like the science methodology, or even understand it, but I am sure you can appreciate it when you buy things and travel, without standardisation and agreement, nothing can get done.

The arguement that we have been building for thousands of years is pretty poor, where are all, not just some, of these old buildings.

Estimation is a major tool in the scientist bag, we use it to establish whether something is close to correct, or total bollocks.

Have a listen to this week's More or Less on radio 4, they had s great example of estimation.

The real problem is that most people did not receive a good science education, and this is costing, in cash terms, billions.

A quick estimation of £1bn is 15 quid for each person in the country.

[SteamyTea]

38 minutes ago, JSHarris said:

Thermal inertia is pretty much the same thing as the thermal time constant, in practical terms.

It is the same thing after a bit of algebraic rearrangement.

It is why I like it.

With a bit of extension it can take shape into account.

[andyscotland]

@JSHarris @Sensus I'm not an architect, and my physics could charitably be described as "hazy".

 

But reading this it sounds like it might be one of those where you're both right, but @JSHarris is more right in practical terms?

 

In my head an analogy might be if you 

wanted to stabilise the pressure in a pipe. You could connect a sealed air-filled expansion vessel. Or you could attach a water-filled reservoir.

 

There are clearly measurable differences in the mass, density and compressibility of the air and the water (and, therefore, the amount of potential energy each vessel stores).

 

But in practical terms, the size of the pipes to/from the vessels would also have a significant effect on the pressure-stabilisation characteristics of the system. A huge head of water up a narrow pipe would work less well than a small volume of air on a big pipe. I think?

 

So it seems to me like the concept of "thermal mass" may be similar. Concrete may well be able to store a larger quantity of energy than timber.

 

But (as I think @JSHarris is saying), the way the materials work to stabilise temperature gain and loss in a building is much more to do with how, and how fast, the materials absorb and release that energy than about their storage potential. And therefore the difference between timber frame and masonry may not be as significant as you'd imagine if you only consider their storage characteristics.

 

If my cod physics has opened an unrelated can of worms feel free to ignore it ?

 

[Jeremy Harris]

22 minutes ago, Sensus said:

 

Yes, I thought you would.  ?

 

Even the person who, reputedly, first coined a definition for the key attributes of an architect (literally "chief carpenter") included strength as the first attribute, which implies that architects, at least around 40 BC, must have had an understanding of the strength of materials.  It is not possible to understand strength without having some form of system of measurement units, as otherwise the term has no real meaning.

 

Strength can only be understood if there are recognised and widely understood units for mass, distance and force (including gravitational force).  Without an understand of those units, and in particular the way forces interact with material properties, it would not be possible to build reliable structures.  Some of that understanding may well have been either innate or empirical in ancient times; some may be empirical even now (we just "know" that a single skin brick wall, for example, will stay up as long as it remains below a certain height).

 

If you can put forward some evidence that shows that defined units are not needed, or even not relevant, when describing something that can be felt or experienced, then I think it might help to bridge what seems to be a bit of a gap in understanding.  From my perspective, as a former scientist, I start from the position that if something physical cannot be measured and defined then it probably doesn't exist.  I can't find any meaningful unit of measurement for "thermal mass" anywhere, just unclear and non-specific rearrangements of units of heat capacity, with no mention (as far as I can find) of thermal conductivity/thermal resistance.

 

[SteamyTea]

2 minutes ago, andyscotland said:

the way the materials work to stabilise temperature gain and loss in a building is much more to do with how, and how fast, the materials absorb and release that energy than about their storage potential.

This has more to do with the thermal conductivity.

Materials are odd things, their characteristics are not correlated to mass. So you cannot assume that because something is heavier, larger, more massive, denser, or whatever measure you want to associate with the count of stuff in it, that it will perform as you imagine it should.

20 seconds on Wikipedia, or Kaye and Laby, will show you that.

Always worth a look.

[SteamyTea]

8 minutes ago, JSHarris said:

start from the position that if something physical cannot be measured and defined then it probably doesn't exist.  I can't find any meaningful unit of measurement for "thermal mass" anywhere,

There are loads of examples, one that narked me the other day was Caroline Lucas MP talking about "wellbeing", if she wants to be taken seriously by the world, stop using wooly, meaningless and unmeasurable terms.

She said another word that had no meaning, but I can only remember my dispair and anger.

[Jeremy Harris]

21 minutes ago, andyscotland said:

@JSHarris @Sensus I'm not an architect, and my physics could charitably be described as "hazy".

 

But reading this it sounds like it might be one of those where you're both right, but @JSHarris is more right in practical terms?

 

In my head an analogy might be if you 

wanted to stabilise the pressure in a pipe. You could connect a sealed air-filled expansion vessel. Or you could attach a water-filled reservoir.

 

There are clearly measurable differences in the mass, density and compressibility of the air and the water (and, therefore, the amount of potential energy each vessel stores).

 

But in practical terms, the size of the pipes to/from the vessels would also have a significant effect on the pressure-stabilisation characteristics of the system. A huge head of water up a narrow pipe would work less well than a small volume of air on a big pipe. I think?

 

So it seems to me like the concept of "thermal mass" may be similar. Concrete may well be able to store a larger quantity of energy than timber.

 

But (as I think @JSHarris is saying), the way the materials work to stabilise temperature gain and loss in a building is much more to do with how, and how fast, the materials absorb and release that energy than about their storage potential. And therefore the difference between timber frame and masonry may not be as significant as you'd imagine if you only consider their storage characteristics.

 

If my cod physics has opened an unrelated can of worms feel free to ignore it ?

 

 

 

Pretty much a spot on assessment, in everyday terms, IMHO.

 

Adding material that has lots of heat capacity, be it specific heat capacity or volumetric heat capacity that's used to define it, may or may not have an impact on the thermal inertia of the building.   As an example, lets roughly compare two types of floor construction, a beam and block floor, with insulation above the concrete, and a passive concrete slab floor, with insulation beneath the concrete.

 

The concrete in the beams and blocks will have a significant heat capacity, so will be able to store a fair amount of heat for a given absolute temperature.  However, because the insulation layer will be above this concrete, the rate at which heat can flow into, or out of this concrete to the inside of the house, so changing the amount of heat stored in the underlying concrete, will be small, so that heat capacity will have very little effect on stabilising the temperature of the house.

 

On the other hand, a passive concrete slab, which may well have a very similar amount of concrete as a beam and block floor, and so much the same heat capacity, will behave very differently.  The concrete has a reasonably high thermal conductivity, so will be able to absorb heat from the house, and emit heat back into the house, as the house temperature varies.  The rate of heat transfer will be fairly rapid, so such a concrete floor will be a useful aid to helping to stabilise the temperature in the house, and increase its thermal inertia.

 

Both these houses will have roughly the same mass of concrete in the floor, so both will have roughly the same floor heat capacity, but in one that heat capacity will be useful in helping to increase thermal inertia inside the house, in the other it will have little effect.

[SteamyTea]

8 minutes ago, JSHarris said:

The concrete has a reasonably high thermal conductivity, so will be able to absorb heat from the house, and emit heat back into the house, as the house temperature varies.  The rate of heat transfer will be fairly rapid, so such a concrete floor will be a useful aid to helping to stabilise the temperature in the house, and increase its thermal inertia.

It is also affected by the laws of cooling, so as it gets closer to equalibrium, the time constant lengthens.

But that is true for any material that is solid, fluids can behave a bit differently. Especially if they change phase, but that just means more sums. Not insurmountable to calculate.

Edited September 7, 2019 by SteamyTea
I hate typing on my phone, but the view of the North Cornish coast is better than my parking space.

[Jeremy Harris]

48 minutes ago, SteamyTea said:

It is also affected by the laws of cooling, do as it gets closer to equslubrium, the time constant lengthens.

But that is true for any material that is solid, fluids can behave a bit differently. Especially if they change phase, but that just means more sums. Not insurmountable to calculate.

 

Another thing to thank Newton for...

 

Reminds me of the argument I had years ago with my wife, over whether tea was hotter or cooler if the milk went in first.  I conducted an experiment (as you do) to prove it one way or the the other.  I ended up being right, tea does indeed end up hotter after a defined period of time if the milk goes in first.

 

The reason is that, because the milk near-instantly cools the incoming hot tea, the rate of heat loss from that point onwards is slower, so after a defined period of time that cup of tea ends up slightly warmer than the one where the tea went in first, heating the cup to a slightly higher temperature, and so increasing the initial rate of heat loss.