New maps of Snow loadings for Ireland

.Donegal. · 24-11-2022 12:14am #1

The motivation of this research was to produce maps of the return levels of snow loads at 100m above mean sea level for the return periods of 50, 100 and 120 years for use in building design. These new maps are more representative and supersede the previous map of return values of snow loadings at 100m above mean sea level for 50-year return period.

It is hoped that the detailed explanation of the methodology and the clarification of the rationale for the new maps being more accurate than the preceding map provided here will be of assistance to regulators elsewhere in adopting these new maps in their own jurisdictions.

-Previous map had input from only 10 stations. This one has 33.

-Including stations from Northern Ireland in the data analysis in this research was necessary to avoid snow load discrepancies along the border region when compared to previous maps.

-The maps produced in this research have more representative results and geographical distribution of snow loads than the preceding map of return values of snow loadings in the Republic of Ireland for a 50-year return period at 100m above mean sea level

In the image below, the top map is the previous snow return map for Ireland in a 50 year period at 100m asl. The new updated version is below it.

To read the in-depth version of the report, click Report at the bottom of the page below.

https://www.met.ie/new-maps-of-snow-loadings-for-ireland

Oneiric 3 · 26-11-2022 10:18pm

'Snow loadings'. What does that even mean?

I'd be interested to know what stations they used here the west to come up with those maps, given that no station (as far as I know) report snow, snow totals and how long it sticks around on the ground. Also, The only station that I think is above 100m is Knock.

MrMusician18 · 26-11-2022 10:44pm

https://www.boards.ie/discussion/comment/119926334#Comment_119926334

It means the weight of snow per meter squared at an elevation of 100m

Oneiric 3 · 26-11-2022 11:11pm

https://www.boards.ie/discussion/comment/119926393#Comment_119926393

Thanks.

It is curious though that few reporting synoptic stations in Met Eireann network are actually on or above 100m, with only a scattering of them that actually measure snowfall itself, given that many are now automated.

cnocbui · 26-11-2022 11:25pm

I'd like to know how many roofs have collapsed in Ireland in the past 60 years due to too high a snow loading.

mikewest · 26-11-2022 11:35pm

https://www.boards.ie/discussion/comment/119926489#Comment_119926489

We had a shed roof collapse years ago from snow load and I have had to repair damage to a house roof after snow. We are in a moderate area according to those maps but those maps are s**the.

cnocbui · 26-11-2022 11:41pm

https://www.boards.ie/discussion/comment/119926510#Comment_119926510

I sold a building earlier this year that still had it's original slate roof from 1893. And they were thin slates.

mikewest · 26-11-2022 11:46pm

The original roofer was very good or you're not a neighbour of where I grew up, or most probably both. We had to reroof the home place recently, built in 1925/6 by the land commission

Victor · 27-11-2022 12:39am

https://www.boards.ie/discussion/comment/119926489#Comment_119926489

Climate is shifting. We had 6 weeks of snow in 2010.

Snow loading is more an issue for buildings with flat roofs than sloping roofs, although roofs with parapets can have issues also. Flat roofs are a lot more common these days than even 60 years ago.

Gaoth Laidir · 27-11-2022 9:08pm

A snow-loading of 0.5 kN/m² is the equivalent of 51 kg of water, i.e., a rainfall equivalent of 51 mm. With a typical ratio of around 10:1, that would equate to around 51 cm of snow accumulation. I assume these figures are for the whole season and not at any one particular time?

.Donegal. · 27-11-2022 10:13pm

https://www.boards.ie/discussion/comment/119928972#Comment_119928972

From my understanding it’s the maximum snow depths at 100m asl with return periods of 50,100,120 years

In the previous map they had 0.5 kN/m² =25cm.

The formula is in the full report. 1cm of snow depth = 0.02kN/m2 of snow loading

For the 120 year period.

North Donegal up to 45cm

Far SW 15/20cm

Jim_Hodge · 27-11-2022 10:22pm

https://www.boards.ie/discussion/comment/119929250#Comment_119929250

Who measured it, where and when? It seems very contrived.

.Donegal. · 27-11-2022 10:30pm

https://www.boards.ie/discussion/comment/119929284#Comment_119929284

It’s for the future. The previous one was full of discrepancies. More stations (33) used this time compared to (10) in the previous one etc: Here’s the full report. Explains it better than I can

https://www.met.ie/cms/assets/uploads/2022/11/Mateus-and-Coonan_2022_Snow-loadings-at-100m-above-mean-sea-level-in-Ireland.pdf

Gaoth Laidir · 02-12-2022 4:06am

https://www.boards.ie/discussion/comment/119929250#Comment_119929250

So they're taking a wetter snow ratio of 5:1, which is probably wise given the slop we sometimes get as snow.

M.T. Cranium · 04-12-2022 7:13pm

I live in a region with perhaps twice the snow loading potential and also one where it is regularly seen rather than having long intervals between occasional cases. So the preferred building design around here is highly pitched roofs with some thought given as to where snow loads will slide off, so a better design would have entrances to homes situated at diagonal corners with an obstruction of some sort to divert snow away from falling on your entranceway. I also note that some older buildings did not clue into this necessity so they are more susceptible to problems but the original generation of builders (let's say 1890 to 1920) in this region anticipated heavy snowfall and if they went with flat roofs at all there was a lot of support built in. These flat roofs don't collapse but at their age they tend to leak. The preferred roofing material for the highly pitched roofs seems to be red coloured corrugated metal. The pitch can be quite high, at least 45 degrees, sometimes a bit more.

Victor · 04-12-2022 7:40pm

A downhill gable would be useful to reduce snow at an entrance. Hopefully it would also avoid having a cross-slope ridgeline.

Flat roofs are popular in some snowy places, so the snow can act as extra insulation and reduce the height of any cross-slope ridgeline.

New maps of Snow loadings for Ireland

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