Shed conversion

[jpadie]

Hello all

I mainly tinker with microelectronics and am a little out of my depth with construction.  But I'm going to plough on come what may.  

Before I make too much of a Horlicks I'm hoping for a couple of bits of advice.  

Briefly there's an existing 4*2.5 shed that I want to convert to a garden office.  It's been standing 60 years or so. I've yet to pull up the floorboards but it looks like it is sitting on bricks on the earth

 

The wall studs are all 50mm deep.  Overlapping horizontal wood cladding onrhe outside.

 

The roof is felt on OSB with some timber joists.  It's not got any support from the apex to the eaves so I need to add some struts.  Probably 2*4s 

 

There is some poorly stuffed mineral wool insulation in the wall cavity at the moment. No breathable membrane but there is heavy plastic sheeting on the inside of the cladding (stapled to the inside of the joists which leads me to believe it was added as an afterthought.

 

No insulation in the roof and the windows are barely present.

 

I'm looking to put some foil backed foam on the walls (50mm) and ceiling (100mm). Then some thin osb then drywall.  The reason for doubling up is to allow a bit more flexibility in installing shelving and desk units etc.  Does this seem sensible?  Is the plastic sheeting "good enough" or should I pull down the cladding and put tyvec up?  Will the felt suffice in lieu of a breathable membrane?  I could put tyvec up on the inside of the osb if not.  

 

Floor: I'm thinking of jablite with chipboard and then some engineered light wood or similar.  I'm unsure how to fit the jablite at the moment as I suspect that under the floorboards there is a void to the earth.   So nothing to bed the jablite onto.   Not sure whether there is a common workaround for this?

 

Windows will be replaced with double glazed pvc units.  I will post again for these as I am not sure how to measure up yet.  I'm struggling with the door too as it is currently very short and I cannot see any off the shelf product that offer small doors.

 

By the by I'm thinking also of installing a reversable mini split with an air-water heat pump for heating and cooling.   Probably a 2btu size but TBD.  

 

Anyway that's enough questions for now.  All thoughts welcome!

 

 

Edited July 24, 2023 by jpadie

[Temp]

Welcome.

 

I think I would remove the existing insulation between studs to create a 50mm ventilated void to reduce risk of condensation. Fit 75-100mm foil covered insulation on the inside and tape up the joints with foil tape to form a vapour barrier. Then OSB and plasterboard for a decent finish or just plywood and paint. 

 

Not sure about the floor. How deep are the floor joists?

 

Edited July 24, 2023 by Temp

[jpadie]

Thanks for the response @Temp

 

The floor is 50mm square sections resting on brick going the width of the shed.  On top of that there are 35mm square sections going lengthway. Floor boards on top of that in some of the shed.  Board on other sections.  

 

When you say remove the insulation and replace with foil backed foam are you suggesting packing the foam between the joists or attaching to the face of the joists?  

 

[Temp]

6 minutes ago, jpadie said:

When you say remove the insulation and replace with foil backed foam are you suggesting packing the foam between the joists or attaching to the face of the joists?  

 

Attaching to the inside face not between. Much easier to get the sheets up tight against each other with no gaps.

 

Mobile phone reception might be an issue due to the screening effect of the foil. Depends how big your doors and windows are and the orientation to the transmitter mast.