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Portal Frame House


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Hello @Marlin


That's a good first go at a concept. I see you have picked up on the inline purlins.. for a domestic type application that makes sense particularly if the frame is to be kept on the warm side of the insulation envelope. There are many reasons for this, some relating to the Architectural design some to do with the structural design and a lot to do with insulating and detailing. There are certain nuances that apply to domestic design. Long story so won't explore in depth just now.


Structurally you seem to have a suspended ground floor, there are other options such as a ground bearing slab.


What you have there structurally is a half way house between a true portal ( two columns / two rafters) and a tied portal ( two columns / two rafters tied at the eaves joint) which is a different animal. One way to think of what you have is akin to a portal frame with an integral mezzanine floor. This too behaves in a slightly different way but it's no great drama.


Your soil type does not appear to be a big issue so standard pads under the columns look to be the likely outcome.


I can't see your bay size but it looks about 4.0m? A 140 deep purlin looks on the ball park. You can play with the thickness. Also you can play about with the number of frames you need, maybe larger bays to fit the intended openings?


For me, if I was designing this for you I would want to look first at the Architectural intent, planning constraints,  then have a quick sizing of the sections, foundations and any key detailing that is off piste. Iterate the design process.. then do the final structural design and detailing once you have the go ahead prom the planners.











Edited by Gus Potter
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Thank you for your comments.


Yes, I have considered timber frame but if done on site that would be very labour intensive and a lot of exposed work before watertight.

I have worked on many Building sites where there has been no effective management and the trades were all tripping over

each other and deliveries were just being dumped (and generally stolen..).. I hated it.. And the sooner Plastering

is made a criminal offence the better..  (Yes, there are alternatives..)


After having no success with hiring a designer for Steel Portal frame, I relooked at a Portal made with LVL's and is certainly feasible..

Some concern about the Columns but, labour aside, probably cheaper than Steel.  (Prices being all over the place at the moment.)



Hardly a first draft.. I have been on this project for over 10 years and have gone back to square One many times.

I started with a Ridge Beam and after looking at others Plans realised it wasn't neccessary with Purlins so close.

My limitations is a lack of knowledge about the Topics you mention.  My Design has been based on my knowledge of the Building Trade and Building Reg's.

I have always wanted a sit down with someone who can advise on issues like 'Architectural Intent' whose meaning I can only guess at..

As to 'Quick sizing of the Sections'..  Welcome to my loop of disappointment..


My guiding principals have been..


As litle concrete as possible.. No Slab. Using Pads or even Ground screws.. (as my potential site may have difficult access for heavyside deliveries). Also Sustainability..

I wanted to get to watertight as quickly as possible.  A simple steel frame and composite cladding/roofing I feel could be achieved in a week (with a Spider crane/Hiab & some luck..)

Minimum Trades on site. Once the Frame and Covering is erected and secure (by the Fabricators hopefully), then a couple of Competent general Tradesmen could complete the rest over a few weeks.

A suspended Ground floor has advantages.  By adding weight to the Frame..  Offsetting Uplift.  I can run services around in the oversite area.  Minimise potential Flooding damage.

With a Steel Frame there is a possibilty for future floor level Beam alteration (Subject to SE of course). 

Potential for using Alternative Materials.. IE.. Industrial  Racking Beams as Joists..    ReCycling is encouraged and approved now..  Even used Coldroom Panels for Insulation.. overclad..

  I certaily considered Mezzanine framing as it has all the Weight Loadings attached and just needed to extend the columns up.. and hey presto... A mezzanine in a field..yay

I thought I might Use Multi-foil as Ground floor Insulation. Just pin it over the joists and add Flooring sheet on top..  Rather than PIR boards which would have to be suspended between joists.. Just an idea..


Whether better for 4 or 5 Frames..?  3m or 4m Bays..  (Build Footprint  100m2  8m x 12m) ..  Will take advice there.           Liked the idea of 12m long LVL 45 x 200 Joists for ease of installation.  I Have not used LVL's so unsure of possible downsides..


So/:  Still looking for a Professional to help me..


I wonder what the Queen's next Jubilee will be called..  Mabey something Organic..  Tree jubilee or Seaweed..  Wait and see..

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