Balsa Core Insulation [Need Some Help Understanding it]

[rxylab]

Hi there

I'm an architectural student and I've got a design that revolves around the boating structure, but I don't understand how balsa core insulation is laid or how thick it would be in order to achieve a good amount of insulation.

I've searched quite extensively through books and websites but I haven't found a certain 'medium' for thickness. The project I am doing is about a student living pod which is 3.2m x 3.2m x 3.2m, to give you some idea of the design. I am using a monocoque laminated wood structure.

Any help would be brilliant, Amo

 

[Phoenix of Hamble]

Its not used for insulation really, its used for mechanical strength against light weight....


Take a look at websites from the manufacturers/products such as Duracore, or Duflex as starters...

 

[wongaero]

Dunno, guess you want the thermal conductivity of balsa - guess being natural, it doesn't come with a data sheet!!

 

[wongaero]

Uh, ok, so it does:
http://www.matbase.com/material/wood/class4-5-10-years/balsa/properties

So I guess being an architect, you can get the thickness from the R value you want, using:
R = l/ k
Where: R = the thermal resistance per unit area of the piece of material (m²K/W),
l = represents the thickness of the material (m), and
k = represents the conductivity of the material (W/mK).

hey, this is fun!

 

[bazobeleza]

You can look up the R value of balsa in the AJ metric handbook a quick calc will give the U value for a given thickness.

However i'd look at some of the newer insulant boards, try kingspan you could laminate that to timber and it has a built in vapour barrier to counter interstitial condensation. laminated between timber it would also have some mechanical strength.

Also don't forget to include the resistance values for the thickness of laminated timber in thermal calcs, every bit counts, including surface resistances.

Good luck with your project (takes me back 30 yrs)

 

[rxylab]

Thanks for the data and the formula Wongaero, I've done the calculations as:

0.1m / 0.07 = 1.43m²K/W

I'm using [at the moment] 100mm of insulation. Then I converted the r value to u value, as:

1 / 1.43 = 0.7W/mK

0.7 is amazingly high, as the sufficient u value is 0.32... I'm doubting my calculations, as I haven't done u/r values in a while. Is 0.7 right?

@ bazonbeleza, Thanks for the kingspan name its amazingly helpful.

 

[wongaero]

Hehe, I'm an electronics engineer who can google things I wouldn't know what numbers are sensible! I guess wood's a pretty good insulator though...

 

[rxylab]

haha, I have run it past a friend and they said it seems right.

 

[bazobeleza]

Ah the students elementary mistake with U Value's.

Us are watts, per metre squared per degrees celsius temperature difference between inside and outside of a structure. It tells you how much energy transferred between inside and outside of structure for a given temperature difference.

Low is good high is bad. U values of 0.7 are what was acceptable for domestic buildings in the 70's

down to 0.32 as you say at the moment. You need to beef up your insulation

 

[snowleopard]

As an architecture student you will be familiar with common practice for insulation houses. For example to get down to a U value of .3 for the walls of my recent build I have 100mm of expanded polystyrene incorporated. Typical thicknesses of Celotex for a roof are in the range 150-220mm. I would therefore expect 100mm of balsa to be no better, after all it is not primarily an insulating material.

In boat construction it is used to provide rigidity in large flat panels and is commonly used in thicknesses of 10-25mm.

I would say you are re-inventing the wheel here. Just buy your SIPs off the shelf.

You might consider incorporating a layer of Tri-Iso which can give you a U value of .18 with a thickness of around 20mm.

 

[rxylab]

Thanks for pointing that out snowleopard. I was asking particularly about balsa core because a tutor recommended it me, I was baffled by it and didn't understand how it would work. But from this thread I know understand that it is for structural purposes.

@ Bazonbeleza, I did also figure out that the u-value should be low and not high, after posting my calculations on here. 200mm of insulation is just too much, for what I have to design for. I'm just going to go with snowleopards and your recommendations.

Thank you to all have replied, it's refreshed my architectural knowledge after not doing much designing for the past 2 months.

Thanks again. : ]

 

[wanderlust]

We have medium weight balsa R value as 0.06 on our database. Low density is 0.05 high density is 0.07. Hope this helps.
If you need actual U values calculating for a structure I can do them on a software here at work. Current minimum U value to meet Regs is 0.35 w/m2 degC