Solid Shed build,vapor barrier question

[TheTiddles]

You want brick then! If someone can smash through a single layer of wood, two layers won’t stop them

And your doors and windows are weaker still

 

[MikeG.]

...... this is literally just a shed that wont be heated.....

Why do you want insulation then?

 

[yuzi87]

With a lot of expensive kit in the shed i dont want moisture getting in etc.

I am leaning towards just the skin inside but do i even need the vapor barrier if its not heated? If i had two skins your saying moisture wont be able to escape from in the frame, but wouldnt vents on outer skin behind membrane in each section of frame help airflow and dissipate moisture?

 

[TheTiddles]

I think you are getting a bit confused.

If you don’t want moisture getting in, you need to seal it shut with some desiccant inside and never open it again, seems a bit of a waste.
Or...
You need to desiccate the air perpetually with either heaters or dehumidifiers and then push that humid air or condensate out mechanically, this is called a tumblr dryer.

Alternatively, the usual method has been described, you are at liberty to try something else.

All sheds are heated, unless you put them in a cave.

Aidan

 

[owen]

I can't understand how you would get interstitial condensation inside a shed without there being a shower/ tumble drier etc in there to make the air humid in the first place.
Aren't most timberframe homes built with osb on the inside and the outside? Are they all wrong too? Genuine question this by the way, I have no experience of timber frame homes having worked in old/listed buildings the last 15 years.

 

[Inspector]

Modern timber frames here (big timber mortice and tenoned) are often skinned with SIPs, (Structural Insulated Panels) That usually have OSB bonded to styrofoam or similar foams on inside and outside. The inside would usually get drywalled inside and house wrapped outside then strapped and sided. The styrofoam is not only insulation but the vapour barrier as well. SIPs can be used pretty much by themselves to build a house without the need of a timer frame. That's what I wanted but talked out by the builder in favour of double wall construction. Shouldn't have listened and found someone else. SIPs get used on timber frames as they can be had in panels up to 28' long x 8' high and up to 12" thick with all the doors and window openings pre-cut by large CNC routers at the factory. They span the distances of the timbers well and are fast to put up (1 to 3 days). They are much like the insulated metal and foam panels used to build refrigerated warehouses for the food industry but the OSB SIPs are better suited to make a house with. They are so tight that whole house ventilation is needed to keep the air fresh and clean.

If you are talking about stick built (2x construction) houses that's a different beast.

Pete

 

[Hornbeam]

Understanding humidity, relative humidity and condensation risk factors is a science but there are some very simple approaches
In construction if you have a cavity filled with a loose fill insulation, it is virtually impossible to fully seal it so allow it to breathe out. If you do seal it fully you will have sealed in an amount of moisture at that temprature/humidity. On a colder day the air wont hold that much and you get condensation/ mould rot
With SIP panels that are usually PIR foam (dont touch styrofoam or polystyrene due to fire risk) the foam is closed cell and doesnt allow vapour movement so you can construct with a solid construction
With either construction you will be putting on an external cladding which again must allow air movement
If you want a further layer for security then you could build as
Internal OSB, Stud frame with quilt. breather membrane battens, profile steel sheet laid vertically with vented filler blocks top and bottom to allow air movement behind steel sheet and air to breathe out of the insulation cavity. OSB provides internal air tightness layer. Always place a separation layer such as dpc membrane between steel and timber due to tanning/chemical treatments of timber and corrosion risks

 

[yuzi87]

Thanks Hornbeam for the great breakdown of information, so just to clarify, could i not build osb/dpc/frame+insulation/osb(with vents in each frame section)/breather membrane/battons/cladding?

Or if i did just do the one internal osb wall would i even need the dpc as its more of a storage shed than a regular workshop/heated room?

Thanks in advance

 

[yuzi87]

Some progress pics

 

[That would work]

I like this idea. And glad that you finally got a measured and civil response!

 

[yuzi87]

I like this idea. And glad that you finally got a measured and civil response!

Which idea do you like mate?

 

[That would work]

The wire mesh as security

 

[yuzi87]

The wire mesh as security

Oh I actually used it under the floor frame to stop any mice/rats getting in insulation lol

 

[MikeG.]

The wire mesh as security

I do that around the walls of bikes sheds for security. Stainless steel EML rather than galvanised. Pointless, of course, unless you also have a steel door and high security locking system.

 

[That would work]

I keep most of mine in a large understair cupboard :wink:

 

[MikeG.]

We've 7 bikes, I think. That'd be some pretty impressive stairs! :lol:

 

[That would work]

Front wheels out and hung up... 4 in there and two in the kitchen at night. It's quite an operation at times. Need just one more tho....

 

[Hornbeam]

I can't understand how you would get interstitial condensation inside a shed without there being a shower/ tumble drier etc in there to make the air humid in the first place.
The issue is not about humidity it is about relative humidity
All air contains water vapour. The amount of water vapour that can be held depends upon the temperature. The warmer the air the more water vapour it can hold
So back to the shed on a moderately warm damp winters day the air will be fairly saturated with water vapour and this air will slowly permeate into the cavity. If we then have a cold clear night the air temperature and the temperature of the outer surface of the shed will drop.
If this temperature drops to a point such that the air can no longer hold all the vapour that was originally in it and so the water condenses out. The temperature at which this occurs is known as the dew point

 

[yuzi87]

The wire mesh as security

I do that around the walls of bikes sheds for security. Stainless steel EML rather than galvanised. Pointless, of course, unless you also have a steel door and high security locking system.

I'm in security, so alarm, magnetic lock, cctv, beam sensors and smoke cannon will protect mine 8)

 

[yuzi87]

Can somebody still answer my question whether air vents in the outer osb skin will help solve double skin problem?