Wood fibre vs wood wool

[Ciaransmith]

Afternoon all,

First time poster, long time lurker.

We have just moved into an old limestone property, circa 200 years old ish. Everywhere is gypsum plaster, which will all being knocked off.

My question is would i notice a difference if i used 25mm wood wool boards over wood fibre on external walls? The people we brought the house from brought a load of 25mm wood wool boards to do the work just never got round to it. So im thinking of using these on all external walls in the house then lime plastering over. Anybody done this with wood wool? Our walls are about 1-1.5ft wide. Ive read that wood fibre are about db better insulation but these are here and free

Can somebody give me a idea of ok to use vs buy wood fibre and find somewhere else to use these.

Thanks C

 

[a twig]

Lists of useful information in this thread covering both wood wool and wood fibre insulation options and installation methods

 

[a twig]

I was very happy with the wood wool boards done with the method outlined in that thread - made a noticeable difference to the warmth of the place

Yes wood fibre is more insulating but if you have a pile of free wood wool boards that for me I would crack on with those, they are also easier to skim over in my experience as they have less give.

 

[Cubist]

Whilst I have no specific and relevant technical experience regarding the use of wood wool boards, I would argue in support of Twigs comment above merely because, for you to do otherwise, would be to fail to exploit an extant, however indirect, 'Sunk Cost' in the shape of the POs investment. What might you otherwise do with the boards you have? Hopefully, not bin them.

 

[Ciaransmith]

I wont be binning them. It looks like ive got enough to the entire house, both internal and external . I was just enquiring to if it actually makes much of a real world difference, if so ill use them for internal and ceilings .

 

[Cubist]

Waste not want not...Bird in the hand...etc., etc. Frankly, unless you come across an alternate material that is orders of magnitude greater/better in terms of its performance, to me it's a no brainer if you can't sell or re-use what you have. Good luck and keep us posted.

 

[Ciaransmith]

Well i could always sell what I've got and get wood fibre, but looking at twigs response it doesn't make sense too.

I wonder if anybody has actually replaced wood wool with wood fibre. On face value is seems better performance but hard to actually confirm in pounds, shillings and pence what the better performance means

 

[a twig]

If you are prepared to headbutt a spreadsheet into submission - the methodology to work it out would be this (lifted from elsewhere):

Since you asked for the how to - this is the formla on how to calculate a payback in years:

Years to Payback = (Ic × Ri × Rf × Eff)
(Ec × [Rf - Ri] × HDD × 24)

The cost of your energy is one factor in determining payback for any energy efficiency improvement, including insulation. To figure the energy savings, use your current fuel costs for both electricity and your heating fuel that you use in a year and put your cost into the above formula.

Ri = Initial R-value (before adding additional insulation) R values of insulation can be found at: powertochoosehq.com/home-3/resources/r-values-various-materials/
Rf = Final R-value (after adding additional insulation)
Rf - Ri = R-value of the additional insulation added
24 = Multiplier to convert HDD to heating hours (24 hours/day).
HDD = Heating degree days/year. This information is easily obtained at Heating & Cooling Degree Daysfor the weather in your area.

To calculate your payback, you have to supply the following:
Ic = Cost of insulation in $/sf (sq. feet). Collect insulation cost including labor, equipment, etc. In other words – total cost.
Ec = Energy Cost in $/Btu.

To calculate the cost of energy, divide the actual price you pay per gallon of oil, kilowatt-hour (kWh) of electricity, gallon of propane, or therm (or per one hundred cubic feet [ccf]) of natural gas by the Btu content per unit of fuel.

To figure the price you pay per unit of fuel, take the total amount of your bills (for all fuels used) during the heating season, and divide it by the total number of gallons, kWh, or therms you consumed during those months. Use the following values for fuel btu content and use the total amount spent combined.

Fuel Oil = 138,600 Btu/gallon
Electricity = 3,413 Btu/kWh
Propane = 91,000 Btu/gallon
Natural Gas = 103,000 Btu/ccf or 100,000 btu/therm

Eff = Efficiency of your heating system. Have the efficiency analyzed by an energy assessor or use the following approximations: gas, propane, and fuel oil systems this is the AFUE (Annual Fuel Utilization Efficiency). Typical AFUE values are 0.62 to 0.87 for oil or propane furnaces, and 0.7 to 0.94 for natural gas furnaces. Older systems being usually somewhat less efficient. Use Eff = 1.00 for baseboard electric. For heat pumps, use the COP for Eff; where Eff = 2.0 to 2.5 for conventional and Eff = 3.1 to 3.4 for geothermal type.

This formula will provide a close answer in years to payback, but the accuracy should be considered to be +- 10-15%, for the reason that the inputs in the formula have their own variable accuracy.

 

[a twig]

Given your woodwool is free - the payback will be massively in favour of using that

 

[Ciaransmith]

I'll just stick to using the free wood wool, seems like abit of a pain to calc properly

 

[Kearn]

I'll just stick to using the free wood wool, seems like abit of a pain to calc properly

You can easily compare the thermal properties of the varying products online; wood wool hardly has anything to offer, it is effectively a render carrier with great key for plaster. Wood fibre comes in many thicknesses, offers more thermal benefit, but not as much as wood batts/sheepswool, and can be a bugger to plaster onto as it doesn’t have much key so you need a nice sticky mix almost hurled on.

However, in your situation, I don’t see the benefit. In fact there is a potential risk.

Walls that thick, if dry and nothing modern inside or out, will be great insulators in their own right, as long as the house is kept at a low consistent temp and you’re not trying to heat up stone on demand. Think of the walls as a nice big thermal store.
Adding a few mm internally isn’t going to change the total thermal mass which needs to be a continuous solid mass. This means you’ll likely have to plaster your uneven walls first before attaching the boards only to plaster them again. You may as well just plaster straight into the stone and leave it there. If you leave air gaps between boards and stone, there is the risk of cold pockets which reduce the insulation properties but also can result in interstatial condensation.

 

[Kearn]

In terms of what to do with the boards and why they bought so many, well…

They have their uses, I’m going through them like crazy right now rebuilding panels.
I’m sure people would buy them, but… transport is a big barrier - logistics and cost. Especially as they are 25mm, not 15mm which makes them more cumbersome and takes away 20mm of insulation room when using for panel infills for example.

 

[lizziecupcakes]

I wouldn’t mind some free left over wood wool!