However this method of mini-spline does not have the inherent beam strength so we propose to use an FRP I-beam as the 6m length across the top of the wall structure. The I-beam can be attached using screws through the MgO – recognizing that the screws will need to be screwed below the surface of the ceiling and then filled to make a flat ceiling finish.
The insulation layer of the Roof SIP will of course be different heights for water shedding slope, and the spline holding the two sections together does not have to extend across the entire roof including eaves, but can go from the wall to wall span.
My calculations are that for a 6m span the height of the I-beam at the wall should be 100mm high. H-beam shown can be
100*100*80*5.5 Width A(mm)*Width B*(mm)*Height C (mm)*Thickness T (mm)
Load tables for this profile are attached.
Note that the SIP gable will add to the strength, as will the MgO as it effectively increases the H-beam width from 100 to the width of the SIP.
From the UDL of 180 we can see the roof will support a person of average weight plus rain, leaves etc. Snow load would have to be calculated.
UDL ratio: L/180
- Deflection limit δ = 6000 / 180 = 33.33 mm
Allowable UDL: ~0.36 kN/m
Bending stress at that UDL: ~14.0 MPaAllowable center point load: ~1.64 kN
Bending stress at that P: ~14.0 MPa
INSTALLATION:
Place one side of the beam on each load bearing wall positioned as per plan. Side of the roof SIP is placed over edge of existing wall to the agreed eave width.
Other side of the beam is screwed into through the MgO to the center point.
Ensuring tight fit in the middle second half (mirror) of the gable is installed and screwed into H-beam
Repeat for each gable section.
Given this strength for the roof – using the same method can be considered where there are load issues on a wall – such as hurricane, tornado etc
Why not?
The argument presented is that the external finished facing (exterior cladding, sprayed waterproofing spackle, ACP etc) does not want to show screw holes, which in salty environments will rust even if SS
HOWEVER it is possible that screws of the correct length screwed through the inner MgO face could go through the FRP H-beam without coming through the exterior MgO
The other factor is cost.
Comparing Cam Lock to a length of H-beam spline – which is more expensive?
Indication are about for a pultruded in standard resin at modest MOQs. That range comes from (a) typical EXW quotes for pultruded profiles and (b) the section’s weight per meter.
Typical EXW for generic pultruded FRP profiles is . made-in-china.com
Many FRP I/H-beam listings show prices spanning roughly depending on spec/MOQ (teaser prices at the low end, realistic small-lot prices at the high end). Alibaba+2Alibaba+2
- Your section area is ~1,479.5 mm², so the weight is ≈ 2.81 kg/m (ρ≈1.9 g/cm³). Multiplying by per-kg pricing gives a budgetary EXW:
$2.5/kg → $7.03/m
$3.0/kg → $8.43/m
$4.0/kg → $11.24/m
$5.0/kg → $14.05/m
(Manufacturers often quote EXW/FOB explicitly for FRP profiles.)
Cam lock prices in China:
EXW (China) for a steel “cam-lock” (eccentric hook) used inside SIP/cold-room panels, ~60 mm size:
$0.50–$1.00 per set at bulk MOQs (hundreds–thousands).
czxxyzl.goldsupplier.com
$0.30–$0.80 per set shows up on some factory listings for large orders/stock models.
sales-quenta.en.made-in-china.com
$2.50–$10.26 per piece is common for heavier-duty or small-MOQ “double-hook” versions (and/or stainless).
Alibaba
“Per set” typically = cam + hook + pin/receiver; pricing slides with material (galv. steel vs 304/316), hook style (single/double), plating/anti-corrosion spec, and MOQ.
“Per set” typically = cam + hook + pin/receiver; pricing slides with .
