Javelin Restoration - Project B

[Forumadmin]

Jack and Amy assisted moving the two halves of the roof frame into place and then we joined them up. Jack fixed the supporting posts to the walls whilst I aligned and leveled. Mosts of the posts are now in place, but the additional purlins need fitting. Hopefully, the weather will hold up and allow this to be done in the week; but with it now dark at 5pm any evening work will have to be by floodlight.

So the aim for next weekend is to get the roof sheeting on.

[p.p.]

good luck to the builder's.... hope for nice weather all the best from switzerland....

peter

[Forumadmin]

Jack assisted last night to complete the roof frame.

[Forumadmin]

Simon. joined Amy and Jack for the roofing party. After we discovered the sheets were 30mm too short an extra 45mm batten was inserted on the wall plate. Progress was rapid with all the panels in place in 2 hours. A break for lunch and I was back finishing off the fixing along the centre purlins and the edges followed by the flashing on the fence panels after dusk. A check this morning showed I only missed a couple of end caps.

TOPIC Pictures on the Gallery.

[Forumadmin]

There has been some progress over the last month with the roof complete, and most of the sides at least water tight, but not airtight. The door is fitted, complete with a sign brought back from the USA by Joe. I have started fitting and sealing the vapour barrier and cutting some of the 50 8x4 sheets of exterior ply that will make the interior walls and ceiling. Then we can put in the insulation.

Today's acquisition of two desicant dehumidifiers were made operational. These will supplement the existing refigerant dehumidifier that was struggling in the cold temperatures. The desicant variety are good down to freezing.

All we need to do now is get the massive room reasonably vapour tight- first the roof , then the walls and finally the remaining unconcreted floor.

The recent very heavy rain and strong wind proved the structure by only revealing three minor leaks. Two were immediately sealed and the other requires some extra damproof protection that was in the plan anyway. This was good because the leaks were revealed prior to the insulation and ceiling being fitted.

The incentive and target is to get the space ready for a Jowett Technical Day soon in the New Year.

[Robin Fairservice]

Are you putting the vapour barrier against the outside walls, or on the inside of the insulation? The latter is the correct position as it goes on the warm side of insulation. In Canada we have lots of experience with insulation and vapour barriers!

[Forumadmin]

As you say the vapour barrier should go on the inside as this stops the more humid warmer air from condensing when it reaches its dew point. That dew point is usually close to the outside in the UK since we do not have such cold temps. However, it can move to inside the insulation and thus condensation would wet the insulation. There may be some condensation still as the air in the void is warmed during the day (thus carrying more water vapour) and cooled at night (when it condenses on the metal roof). Once again slightly different to Canada where it would remain frozen. Thus I have decided to put a drip trap on top of the insulation in the roof. This will also maintain an air gap above the insulation to allow free flow of air under the metal roof. As there is a roof light every 2 meters, I am putting UV stabilised bubble wrap under these sheets to join with the other layer of membrane which is under the insulation and above the exterior ply to form a vapour barrier. Thus any water in the insulation can evaporate through the void but is also heated when there is any sunlight by the greenhouse effect of the roof light and bubble wrap.

This may not be a perfect solution (spray on foam is) but it is the cheapest. In some places where we need the extra height expanded foam will be used as the insulation.

The whole job is slightly complex as where there are wooden walls I thought it necessary to keep the damp from ingressing into the insulation. So I have put a DPM on this wall, but have left it open at the top to allow the insulation to breathe into the roof void. I will put an internal vapour barrier there as well.
Most of the walls are metal, so here the vapour barrier is on the inside; but I have yet to figure out how this insulation will breathe as all around there is window sheeting above the walls. Condensation on the metal walls does not seem to have been a problem in the past, it was only on the roof.
Note that the position of the vapour barrier is dependent on the difference in temp from the outside to inside. In tropical countries (if it is used) it is on the outside. Putting the insulation (aluminised foam) above the roof is gaining popularity here.

[Robin Fairservice]

South western B.C. is mild and wet, but the insulation is still placed as I said. What I didn't say is that a membrane is put on the outside of the wall. Most residential building construction uses timber framing and the outside sheathing is either plywood or O.S.B., also called wafer board. On the outside of this is placed a building paper, or more commongly nowadays a membrane called "Tyvex", which prevents moisture getting into the sheathing, particularly in windy conditions. With steel sheathing one doesn't have issues with wind or rain penetration, but still need the membrane on the inside of the insulation. Condensation of moisture on the inside of the steel shouldn't be an issue as it should be dry.

The roof space has to be ventilated, and in the ceiling the vapour barrier is placed on the warm side of the insulation.

In the Arctic the inner membrane is sometimes placed within the insulation, but I haven't has any experience of working up there.

I have found that a well installed inner membrane is nearly as good as insulation for heat retention in a building!

[Forumadmin]

I did look at semi-permeable membranes, but perhaps wrongly decided that they would not keep the drips out whilst allowing the water vapour through. I may have been swayed by the cost though! May be, in steady state conditions, the roof void could be assumed to be dry (because of the vapour barrier) , but the common problem here in November is that we have warm days and cold nights with a very misty external atmosphere. This saturated air will permeate into the roof void (via the extensive ventilation that is required) and then in the evening, when the temperature drops, condenses on the metal roof. Thus my plan to keep that saturated air from the insulation by using the upper membrane and also catch any drips that might happen from the quite small volume of air above the membrane. This is slightly compromised by the open end towards the roof light. The alternative was to totally wrap the insulation in plastic.

[Robin Fairservice]

You obviously have a good understanding of your conditions, so the best of luck with you building operations.

[Forumadmin]

We will see. Putting theory into practice is trial and error!

[Forumadmin]

A concerted effort last weekend by Chris and myself almost completed the insulation of the new half of the garage. As recommended a semi permeable (liquid water proof) membrane was put on the top of the insulation and a non permeable membrane or vapour barrier beneath the insultaion. Below that exterior ply protected the barrier.

[Forumadmin]

Now planning the power as the existing 32A supply is probably not going to be enough. Two separate circuits protected by a 63A Residual Current Breaker (RCB) will feed two Miniature Circuit Breakers rated at 32A. These MCBs will protect the separate 50 meter cables into the garage. The MCBs are currently Type B which allow up to 5 times rated current for 100 milliseconds. If the various loads with high start up currents cause tripping, alternative types of MCB (Type C or K) will be used. The loads causing problems may be the compressor, fan, lift, TIG or Spot welders.

The design size of PVC coated cable running in free air at 30 degC (not enclosed) should be 2mm diam or 3.1mm square for 32A max load and has a 6.6 ohm/km resistance which gives a 21v drop at 32A assuming power factor of 1. Note the size of cable currently installed is double this and just about copes with the transient start up loads. 5% (12V) is generally regarded as a max volts drop. I will check the real voltage drop tomorrow and see how theory corresponds with practice.

The two sets of cables will feed separately to two parts of a consumer unit with a 100 A main switch each. This is to prevent circulating currents through the RCBs or MCBs that would cause them to trip and to provide greater detection of a cable fault. An RCB feeds each bank of MCBs feeding the old garage and the new extension separately . 6 Amp MCBs protect the light circuits , 16A MCBs protect the compressor, welders, and lift, and 32 A MCBs protect the 13A sockets in 3 rings. Balancing the current through the various circuits may need some care on who does what, where! It is a bit like running a Jowett on a dynamo with electric fan, wipers and lights. You cannot have all three at once for long.

The garage roof now has an inch of snow on it, so is having its first test!

[Forumadmin]

Chris and I completed the building of the bench and second set of shelves. Chris also erected the Pratts period sign and all the rally plaques. Late evening Amy and then Jack visited and we erected the two post lift. So very pleasing progress. Photos to follow.

[Forumadmin]

The actual drop in voltage was 6v for an 11A load thus about 18v for a 33A load. Prettty much as expected.