Profiled metal sheeting part 2 Profiles and putting it together

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Hornbeam

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Profiles and Cladding systems

Flat painted steel sheet has negligible stiffness and so needs to either be profiled or bonded onto a rigid substrate. The most common profiles available are

Trapezoidal (sometimes called box) profile. This is the most common profile, most readily available as 32/1000 profile. This means that the profile depth is 32mm and a sheet cover width is 1000mm. Different profilers will have different numbers of ribs and the ribs may be different shapes so sheets from different profilers will not fit together. For roof installation the profile should have narrow crowns and wide troughs to carry the rainwater down to the gutter. Wall cladding looks better with wide crowns and narrow troughs. Note you must ensure the top coat is on the correct side of the profile

This type of profile is probably the easiest to install however it can look a bit industrial

Sinusoidal (also known as wrinkly tin). This is a fairly old fashioned profile seen on many farm buildings. The profile is a bit less industrial looking than trapezoidal sheeting but it is more difficult to install as fixing choice and position are slightly compromised. There are also no flat areas to work to

The profile of the sinusoidal and trapezoidal profiles makes them fairly stiff and these would be classed as “self supporting and can typically span between 1200mm and 2000mmbetween supports)

Standing seam. This is similar to some of the copper and zinc roofs often seen on churches and other old buildings. The sheets join together by an overlap joint which either clips together or the joint is physically crimped together. . The sheets have fairly low stiffness and so are aways installed onto a fully boarded structure, with a breather mebrame between the sheeting and the board. This type of system is used in some domestic developments but is relatively high cost. It does however have a very nice appearance.

Flat and microrib profiles. These have minimal stiffness and so are always made into composite panels.

Material thickness. In general I would always recommend 0.7mm for external roof sheets and either 0.5 or 0.7mm for wall sheets. This gives good spanning capability and resistance to impact damage

There are 4 main cladding systems

Single skin. This is a single layer steel. IT can provide a good relatively airtight building, but has negligible insulation properties. Single skin construction can be prone to condensation, particularly at night as the when the temperature drops, the air can no longer hold the water vapour within it and this condenses out onto cold surfaces. One of the most effective ways of controlling condensation is by good ventilation. In general a single skin construction will not be a pleasant place to work in the colder months and there will be a high risk of condensation on tools and machine surfaces. Note this is true of any uninsulated construction not just steel

There is no reason why a steel skin cannot be installed over a blockwork or boarded timber structure, either just as an aesthetic finish or creating a cavity which can be filled with an insulation quilt in much the same way as a build up system. If installing over a timber board then a breather membrane should be installed between the boarding and the sheeting

Insulated constructions. Insulation does not make a building warm. Insulation slows down the rate of heat transfer. If a building is not heated then the only real benefit of insulation is a reduction in condensation risk. As we generally want a bit of warmth when working in the cold insulated airtight (draughtproof) construction will reduce the heating requirement

Build up insulated systems. This is where 2 layers of steel sheets are installed, with a spacer bar and bracket system between them. This generates a cavity which is filled with rock or more often glass wool quilt. These spacer systems can create a cavity of up to 300mm. For most uses I would suggest around 100 to 150mm on the wall and 150 to 220mm on the roof. The inner steel sheet will usually only be a basic white polyester coating, which will be adequate if the space is relatively dry and warm. This is often specified as 0.4mm but if it is in any way likely to get knocked I would go for 0.7mm

This type of system requires a bit more on site installation, but once the initial liner sheet has been installed the inside is relatively warm and dry

There is no reason why a hybrid system cannot be installed with a timber stud construction, using OSB or similar on the inside and a single skin sheet on the outside. Care must be taken to consider moisture vapour movement and escape otherwise this could lead to rotting of timber and corrosion of the back of the steel shhets

Foam composite panels These are produced in a factory where polyisocyanurate foam is injected between 2 steel skins, to produce a complete cladding panel. Roof panels will always have a trapezoidal profile. Wall panels can be profiled, micro ribbed or flat. In general flat and microrib panels are significantly more extensive. PIR foam is a much better insulator than rock wool quilt or slab and so these panels only need to be half as thick for the same insulation performance. I would suggest 60 – 80 mm for the walls and 80 to 120mm for the roof.

Bonded mineral wool panels. These are factory produced where 2 steel skins are bonded onto a rockwool slab core. Generally these panels are either flat or microrib and are only used on the wall. They are very heavy and handling can be an issue, They do have extremely good noise reduction which is often a concern, but you will also need to consider noise through the roof.

Bonded mineral wool and foam composite panels have much greater spanning capabilities. In theory this nmeans that you can reduce the number of intermediate supports. Reducing the number of supports means that the ones which are installed have to be much larger so separation is usually kept to less than 2000mm

Installation.

None of the wall or roof cladding systems are structural and so will need some form of engineered structure to attach onto. For industrial buildings this would normally be a series of portal frame spaced up to 8m apart with cladding rails between. This has foundation implications as all the loads are being taken through the points of contact of the portal frames. There is no reason why a timber stud construction or fabricated frame like the old concrete sectional garages cannot be used, however for anything of any size I would get a structural engineer input.

Steel cladding dependant upon gauge and profile will span up to about 2 metres. Composite panels can span much further but the members they are spanning across will need to be relatively stronger as they are carrying more loads

As per Mikes recommendations in his thread, I would recommend a couple of courses of bricks at the base,

Thin steel sheets can have very sharp edges so decent cut proof gloves are essential. Handling larger sheets is a 2 person job

Basic cladding installation is similar for both roof and walls. Because of the general size of workshops there should be no need for end lap joints between sheets as sheets can readily be purchased up to around 8m,.

Through fix trapezoidal sheeting can comfortably be laid down to 4 degree pitch after deflection. Work on around 6 degrees minimum design pitch

On site cutting. It is best to minimise site cutting by ordering correct length sheets. These will have been cut with a guillotine and the cutting action actually smears the softer zinc alloy coating over the cut end.

Profiled steel sheeting is best cut with a set of nibblers or hand snips, but can be cut with a jigsaw or a circular saw with the right blade. I have found a circular saw and batten produces good results along and across the profiles but you must wear a face visor as it spits bits everywhere. Don’t use an angle gringer as it will damage the coatings Site cut edges should be cleaned to remove any sharp burrs and a clear edge protection lacquer can be applied

If attaching to a timber frame it is best to put a thin strip of barrier tape (or dpc) between the timber and the steel some timbers and timber treatments can be quite corrosive.. Time spent getting everything set out will save all sorts of problems later on. Sheeting is installed using drill drive fasteners which drill a pilot hole and then tap as they are installed. There are different types of fasteners for fixing in to timber or different thickness steel so check you have the right ones. I would strongly recommend using austenitic stainless fasteners as these have excellent durability. Carbon steel is a bit cheaper but will corrode. Fasteners will have an epdm coated washer. If installed straight the washer will form a fully waterproof seal. Generally fasteners are fixed in the profile troughs as this gives a much more secure fastening. The problem with sinusoidal profiles is it is difficult to get good epdm compression. You can purchase fasteners with thicker softer washers or go for a crown fix. I think crown fix for sinusoidal roof profiles is slightly better as fasteners in the trough of the profile will dam the flow increasing risk of leakage.

The drill point of the fastener does create a bit of steel swarf. Remove this as soon as possible with a soft bush otherwise it tends to bed itself into the paint layer and rusts. It isn’t critical but it can look really bad.

Bent steel flashings are used to close of the corner joints and other details.

It is important to consider air tightness as a good airtight building will be much warmer and easier to heat. The key point is to identify the airtight layer and ensure that it is continuous. In general this should be the innermost layer of the construction All joints should have a sealant tape applied. If doing a built up system the tape is applied on the side facing the insulation as it wont be seen. Steel is air-tight so as long as all the joints are well sealed the construction will be airtight. Where a flashing runs across a profiled sheet, this is sealed using profiles filler blocks made from epdm or polyethylene foam which a lightly bonded in place.

If using a hybrid system with a boarded inner skin, OSB is fairly airtight but again the joints between the OSB should be sealed with a gun applied sealant

If installing composite panels (either type) these will have compressible foam seals on the side. Provided the panels are pushed tight up against each other this will produce a water proof air tight seal

For built up systems, once the liner sheet is installed (or if installing over a blockwork or similar structure. Spacer brackets are installed fastening through the liner sheet into a structural element. A closure flashing is also fitted at the bottom of the wall to stop insulation escaping and vermin etc getting in to the cavity Insulation quilt is cut to fit between the spacer brackets/rails and then the outer sheet is installed . Side lap joints should be sealed with a bead of butyl mastic typically 6 X 5 Available in rolls with a release paper. Don’t use gun grade its messy and gets everywhere

Some people suggest sheeting on either side of the structural members, effectively boxing everything in. This can make a bit more space but the gains are limited as any structural steel element bridging between the inner and outer will form a cold bridge or easy path for heat to flow out of the building. I generally don’t advocate boxing things in as it makes it much more difficult to see if there are any corrosion or structural issues developing.

.Where there are junctions between sheets (eaves, ridge, verge) these are closed over with a bent steel flashing made from the same material. The edges of the flashing should ideally be folded back or welted as this produces a much stiffer flashing with no visible cut edges. A drip flashing / which could be a combined closure and drip flashing is installed so that rainwater runs away from the building and drips clear.

The easiest way to provide daylight is through in plane GRP rooflights. Where the roof light is required the liner and external sheet are replaced by a grp twin skin rooflight. If the rooflight does not run the full pitch of the roof, then the end lap joints must be made over a structural element. Cheaper polycarbonate rooflights are available, they do the job but are a much lower quality option. If fitting polycarb in a plastisol coated steel roof a barrier tape must be installed as the plasticisers in the plastisol attack the poly carb and it will go brittle and crack.

Where a window or door is required, the area around the opening must be structurally reenforced. The sheet edges are flashed off to cover any exposed edges and ensure no water penetration. This is probably the most tricky part of the job as the flashing at the head of the door or window has to sit behind the profile and fit with the side closures which fit over the cladding. Just think that water runs downwards and must be directed out, It is possible to fit rooflights in a wall cladding. This is the same as in a roof and much easier than framed windows, however grp is only translucent so you wont get much of a view.



There are quite a few u tube videos on how to install cladding. Some are quite good. Some are awful. In general if you look at some of the reputable manufacturers website there is lots of information available

Maintenance

Well installed it shouldn’t need much maintenance, This can make it a good choice if you are tight up to a fence or hedge, An occasional clean to remove bird dropping or if there starts to be a build up of algae.

Keep an eye on any cut edges as if these start to corrode it is best to treat them early. Because of the type of paints used, if you have to overpaint an area you must use a suitable paint, particularly for plastisols, however this should not be required for at least 20 years

Some manufacturers provide small tins of touch up paints which can be used to repair any small scratches.

Note that site applied overpaint and touch up paints will be a different paint system to the oven cured paint system originally applied. This means that they will fade differently over time. Because of this I would only touch up significant scratches



Costs

I have deliberately not put any cost figures in here as they are extremely variable and in the current climate they would be out of date in a couple of weeks.

The difference between the components for the most and least expensive is probable a factor of 50%, but once you factor in your time and how long you want the building to last I would generally go towards the higher end spec



General recommendations


Unless your workshop is going to be large enough to go to a full portal frame construction, I would probably go for a hybrid construction. The below is in no way a formal spec but is a good starting point

Treated timber stud walls on a brick base with a dpc layer

OSB or White polyester coated steel inner face fully sealed

Mineral wool insulation between the studs. If you have particular noise issues consider using a denser rockwool slab

Breather membrane insulation quilt

32/1000 high quality plastisol 0.7mm external sheet, Note the sheet should be vented top and bottom to allow moisture vapour movement. Matching 0.7mm flashings

For the roof I would use standard 160mm built up construction with 0.7mm profiled steel liner and outer, or 80 to 100mm foam composite roof panel. One of the advantages of the metal liner is it is already painted



I will try and add some images later so people can see what I am referring to

If you have any questions drop me a pm

Ian
 

bobblezard

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Hi Ian,
This is very interesting and informative, thanks.
One question that I have in choosing whether to go for box profile is how strong it is for walking/working on? I want to replace the roof of an attached garage. We have been accustomed to using this roof to access and work on the chimney and house roof. So in effect walking on it and planting ladders. Would this be possible using 0.7mm box section properly installed or is it just asking for trouble?
 

Hornbeam

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There are 2 aspects regarding walking on a roof. Fragility, is there a risk of the roof failing and then falling through the opening. Walkability, will the roof profile bend/buckle resulting in permanent damage to profile. While there are formal tests for both of these criteria, in practice it will depend upon how heavy you are, how "lightly" and where you walk on the profile and how the ladder is footed.
I would say that it could be OK but it depends on where you foot the ladder and putting a spreader board under teh feet. It will also depend very much on what teh spacings are of your sheeting rails
 

bobblezard

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Thanks, yes I guess that's pretty much what I expected. I'm not light at 15st but wouldn't wear steel cap boots, or worse, stilettoes... I didn't imagine much risk of going straight through the roof as thinking of an overspecced frame with both joists and rails on 450mm centres and would hope that profiled steel sheet couldn't deform that much if fixed properly?!
I was more worried about damaging the roof with potential risk of rust/leaks. I guess from what you say it all depends on common sense and a light touch/protection.
I'll consider other options but was drawn to box profile sheets. Thanks again for the reply
 

Ollie78

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I used trapezoidal stuff on my shed. But I did not do it unsupported but on top of 18mm osb and membrane.
The manufacturer told me it required support at 600mm maximum. So I just boarded it and screwed it to that.
I much prefer it to felt. Also I have a bit of the same profile in clear fibreglass to let light in.

I definitely would not trust it for walking on without the osb. I do walk on it to cut back my neighbors hedge each year but try to step on the low parts only.



Ollie
 

Baker1983

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@Hornbeam Really insightful post thanks. I’m thinking of using a single skin metal box profile as my cladding to the rear and sides of my garden room. The build up of the walls will be fairly standard; frame, OSB, breather membrane, battens and then metal profile cladding.
I have a question regarding the battens; Should I fix vertical battens and then horizontal battens or is this not really necessary? Is 600mm spacing on the battens sufficient and Also when fixing to the battens how far apart should the fixings be?
Thanks, Rob
 

Hornbeam

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eally insightful post thanks. I’m thinking of using a single skin metal box profile as my cladding to the rear and sides of my garden room. The build up of the walls will be fairly standard; frame, OSB, breather membrane, battens and then metal profile cladding.
I have a question regarding the battens; Should I fix vertical battens and then horizontal battens or is this not really necessary? Is 600mm spacing on the battens sufficient and Also when fixing to the battens how far apart should the fixings be?
Thanks, Rob
Assuming you are using wall profile trapezoidal sheeting ( wide crowns and narrow troughs, then there should be adequate air cavity for air movement up and down the profiles without having to cross batten.
I would use treated battens and the staple a strip of dpc membrane over the top and down the face of teh batten which will be in contact with the back of the metal sheet.
I would also recommend stainless fasteners screwed through the troughs into the battens
Battens at 600mm centre will be more than adequate for sheeting of 0.5mm gauge and above
Ian
 
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