Build thread- My concrete workshop. Pg4 Bench built.

[PAUL_TDI]

I've been browsing forums trying to search for insulation advice for my concrete prefab workshop but whatever I read raises question so thought I better join a forum and this seems like a fairly busy one with solid info.

So moved into my new house on 1st June and I had compromised on buying a house without a garage as long as it had a garden big enough to build a workshop.

Once the house was sorted I started work...

Base dug out to 6" throughout and DPM was laid before concrete was poured.

I had the ferns cut before workshop was installed

Then voila!











It's a 16'6"x9' with 30" steel door and UPVC throughout, I wanted minimal upkeep so didn't want to need to treat wood regularly.

Insulation wise I was planning on a basic stud work wall around the inside with 2x2 as to not take too much space, the most I'll have directly on the wall are hand tool hangers and those plastic box racks. Then fill the void with sheet polystyrene.

Much the same on the roof aswell, just using a thinner ply to board it out.

My main question is what kind of ventilation should I leave into the insulation space?

I'm using Thomson water seal on the outside and was going to coat the inside too to reduce ingress damp(?)

I was originally thinking of using celotex/kingspan originally but unless some comes up dirt cheap then it's too expensive.

Comments and advice much appreciated!

 

[PAUL_TDI]

Thats annoying, how comes I can't post pictures via PhotoBucket?

 

[PAUL_TDI]

Whoops, suppose I should of read the rules first.

 

[longinthetooth]

Diminishing returns with insulation if you can't insulate what looks like a steel door? Any heat you introduced would just 'urinate' out through that, rendering any other insul. relatively pointless.

I'm assuming that you intend a heat source, even if intermittent?

Following yr studwork idea, I think you should leave a 25mm gap between that & the ribs of the wall panels so that there's a 25mm gap along the internal eaves behing the top of the studwork. This is to provide enough airflow esp since you have no air ingress at slab level. The other thing is to have an internal face that restricts the passage of moisture into the studwork layer. I can expand on that if needed. I'd also use treated wood for the studs and especially their soleplate.

 

[PAUL_TDI]

It's only a single sking steel door so was planning on attaching some baattern, insulating and boarding that too.

Would that surfice?

I'm not looking to make it super toastie but merely try and combat the dreaded damp of concrete prefabs, plus make walls I'm able to drill into and mount smaller items too.

 

[longinthetooth]

Yes you could replace the latch spindle with a longer one and the lock cylinder with one that was longer on one side (assymetrical) - look up some catalogues on-line for available lengths ...

Is doorframe steel also? Hellish detailing!

 

[PAUL_TDI]

Yes door frame is also steel, I wanted fairly good security and this was the best choice away from wood the company offered. It's a Hormann door and frame.

 

[PAUL_TDI]

Ah just read your edited iniatial post...

Yes I was planning on a oil radiator on a stat/timer to help. Yes what do you mean by internal face to stop damp? Would the Thomsons water seal not stop this?

So would I attach the polysterene to the concrete walls or the wooden boards?

At slab level it was recomended to lay the mortar fillet, I'll shortly seal the floor then use Leyland floor paint on it too.

I thought about using sofit vents in the boarded out walls/ceiling to aid ventilation too if need be.

 

[Peter Sefton]

Hi Paul
Welcome to the forum looks like you are getting some sound advice on the methods of insulating, when it comes to buy your insulation you could give these guys a try they sell Kingspan seconds at reduced prices.
http://www.secondsandco.co.uk/
Cheers Peter

 

[longinthetooth]

Ah just read your edited iniatial post...

Yes what do you mean by internal face to stop damp? Would the Thomsons water seal not stop this?

So would I attach the polysterene to the concrete walls or the wooden boards?

At slab level it was recomended to lay the mortar fillet, I'll shortly seal the floor then use Leyland floor paint on it too.

I thought about using sofit vents in the boarded out walls/ceiling to aid ventilation too if need be.

1) 25mm gap between the most prominent internal surfaces of the conc walls and the back of the studs - then insul infilling between the studs eg 50mm studs with 50mm insul. 50mm is light for studwork so pack behind fixings (what fixings I can't quite imagine). Air gap behind studding vents at eaves through corrugations in roof cladding.

2) Internal lining boards to studding ideally need a moisture barrier to prevent moisture in the heated room air room air being absorbrd and transmitted through to the cold side of the insulation where it might condense & rot the studding. Barrier cld be foil-backed pbd or a sheet of polythene ... This is sound practice but your shed may not be as critical an application as a fully-heated dwelling ...

Similar considerations would apply to the ceiling / roof.

 

[PAUL_TDI]

I think I follow...

Basically building a 50mm internal stud work wall, 25mm away from the concrete walls? What about if I reduced the stud work to 25mm and then used a better quality insulation like kingspan which will then foil backed for the moisture barrier.

Would I glue the insulation to the outer wood walls to stop it moving into the air gap?

All I'm trying to do here is get rid of the damp issues to a degree, I can work in the cold.

Thanks for the link Peter, very useful!

 

[longinthetooth]

Maybe better to backtrack & simplify - could you infill the receses in the ribbed conc panels w insul (polystyrene or pu foam boards)? Forget about the venting business & hope for the best. With minimal / intermittent heating its a borderline situation less demanding than a fully-heated dwelling. But I WOULD ventilate above any ceiling that you put in, & looking at the apparent ingress of daylight in the photos, the roof corrugations would seem to provide this.

 

[PAUL_TDI]

Thanks for bearing with a dumbing down I thibk I shouldof mentioned I'm not a master at wood craft the space will be for my RC cars and normal car stuff.

I like the above plan, much cheaper and less space used.

RE....the eaves ventilation, should I let the wall boards meet the roof boards so there's some ventilation then going down the walls or leave a gap for the eaves to vent into the room?

I can afford to loose an extra 25mm in the roof so the insulation doesn't touch the ceiling, thus allowing plenty of air movement up there.

Thanks again.

 

[longinthetooth]

If the eaves vent to the room there's no point in any insulation at all!

The new scheme is to insulate the concrete panels in situ (cut for a tight fit if you're able to, otherwise cut undersize and foam it in round the edges). No venting on the walls.

Ceiling needs venting ABOVE THE INSULATION, the principle is to vent the COLD side of the insulation, which is where condensation occurs, not the WARM side.

Again, there'd no point in insulating at all if the space wasn't going to be heated.

 

[PAUL_TDI]

Thanks for clearing that up, understood.

Yes I plan to get an oil rad on a that in there.

 

[PAUL_TDI]

Any ideas on how to attach boards directly to the concrete sections? The only catch being drilling/screwing into the concrete panels voids my warranty.

I thought about undoing the bolts which hold the panels together and put some kind of strap there to bolt onto, but putting strapping then blindly trying to line up bolts on a 8x4 sheet could be awkward.

Are glues like no more nails strong enough to hold them to the wall and hold light storage on the wood.

I can fix at the top no issues by spacing out a new beam attached to the bottom roof beam.

But i'm lost at a suitable way to mount flat to the concrete. I thought about putting horizontal 1" batten along the bottom strapped to the panel bolts but didn't think it would produce a very strong mounting point?

 

[PAUL_TDI]

Well good news!

I've been told (in writing) by Nucrete that I can drill into the thick parts of the concrete panels without damaging my warranty.

So new plan.... Fill void with insulation, then attach 8x4 sheets of ply directly onto the concrete, it seems 18mm ply is a popular size to get 2nd hand from being used at site fencing. I would probably use 6 screws for each sheet of 8'x4'.

I'm looking at these wall plugs...

http://www.screwfix.com/p/fischer-sx-ny ... 100/90467#

Matched to these coach screws...

http://www.screwfix.com/p/exterior-coac ... tid=137790

Figured they would provide a good strong anchor.

I would coat/seal the back side of the ply.

 

[longinthetooth]

Those conc ribs aren't so huge in section - the fact that you're allowed to drill into them just implies that there is no steel reinforcement inside them. Fixings that are too big / too tight a fit could split the concrete rib even if just locally to the fixing. So I'd forget the 6mm coach screws and use normal woodscrews - say 5mm by 50mm or whatever seems right. Use a depth stop on the drill & go a bit deeper than the length of the screw (less the ply thickness) to leave a bit of clearance at the bottom of the hole.

 

[PAUL_TDI]

Ah yes good point, I was going a bit OTT on the coach screws..... not sure I should admit to what my first choice of fixings could be.

Indeed, thats what the company said, I can drill carefully there as there's no reinforcement.

 

[PAUL_TDI]

Well what with my first sons birth and more important things to do in the new house and having to get a bigger car the workshop hadn't really been touched at all until recently.

So for Christmas my parents kindly bought me most of the electrics I'll need for it....



several metal clad double sockets



And even 40 meters of armoured cable and a handle full of clips.

This spurred me on to splash a bit of cash on it to atleast get electrics in there so I found a local supplier of seconds insulation. I got these 4 sheets of 40mm foil backed for only £48.



So far I have only used 2 sheets doing this...



One of my neighbours was building a conservatory and put 50mm insulation in the floor so with that I did the door...





I've found some ply seconds going cheap so hoping to get about 5 8'x4' sheets of 12mm to get 1 end done as I say to atleast get electrics in, I already have plenty of lights to go up too.

Now for a quick question, would I be able to use expanding foam and some of the 50mm insulation I have left to block the eaves at the peak of the roof? As a lot of tree debris and even worms are ending up on the floor.

So I was thinking of spraying the foam into the eaves and then stick a strip of 50mm insulation in the middle of the roof sheets stuck with the foam..



I'd like to think I'll get round to insulation the roof but can't see that happening for a while as moneys tight.